chore(prlint): update second comment to state exemption request has been submitted (#29000)

### Issue # (if applicable)

Closes #28803

### Reason for this change

If a contributor requests an exemption or clarification for a PR, they will get a second message (due to the comment event) telling them again that they can request an exemption/clarification. This may confuse contributors, especially beginners.

### Description of changes

Detect if an exempt request comment already exists, next comment would mention an request has been submitted and waiting for a maintainer's review.

### Description of how you validated changes

unit tests

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: GavinZZ

tools/@aws-cdk/prlint/lint.ts

@@ -250,7 +250,7 @@ export class PullRequestLinter {
    * @param existingReview The review created by a previous run of the linter.
    */
   private async createOrUpdatePRLinterReview(failureMessages: string[], existingReview?: Review): Promise<void> {
-    const body = `The pull request linter fails with the following errors:${this.formatErrors(failureMessages)}`
+    let body = `The pull request linter fails with the following errors:${this.formatErrors(failureMessages)}`
       + '<b>PRs must pass status checks before we can provide a meaningful review.</b>\n\n'
       + 'If you would like to request an exemption from the status checks or clarification on feedback,'
       + ' please leave a comment on this PR containing `Exemption Request` and/or `Clarification Request`.';
@@ -265,6 +265,10 @@ export class PullRequestLinter {
       });
     }
 
+    const comments = await this.client.issues.listComments();
+    if (comments.data.find(comment => comment.body?.includes("Exemption Request"))) {
+      body += '\n\n✅ A exemption request has been requested. Please wait for a maintainer\'s review.';
+    }
     await this.client.issues.createComment({
       ...this.issueParams,
       body,

tools/@aws-cdk/prlint/test/lint.test.ts

@@ -1039,6 +1039,71 @@ describe('integration tests required on features', () => {
     });
   });
 
+  describe('with existing Exemption Request comment', () => {
+    test('valid exemption request comment', async () => {
+      const issue: Subset<linter.GitHubPr> = {
+        number: 1,
+        title: 'fix: some title',
+        body: '',
+        labels: [{ name: 'pr-linter/exempt-test' }],
+        user: {
+          login: 'author',
+        },
+      };
+      const prLinter = configureMock(issue, undefined, ['Exemption Request']);
+      await expect(prLinter.validatePullRequestTarget(SHA)).rejects.toThrow(
+        'The pull request linter fails with the following errors:' +
+        '\n\n\t❌ Fixes must contain a change to an integration test file and the resulting snapshot.' +
+        '\n\n<b>PRs must pass status checks before we can provide a meaningful review.</b>\n\n' +
+        'If you would like to request an exemption from the status checks or clarification on feedback,' +
+        ' please leave a comment on this PR containing `Exemption Request` and/or `Clarification Request`.' +
+        '\n\n✅ A exemption request has been requested. Please wait for a maintainer\'s review.',
+      );
+    });
+
+    test('valid exemption request with additional context', async () => {
+      const issue: Subset<linter.GitHubPr> = {
+        number: 1,
+        title: 'fix: some title',
+        body: '',
+        labels: [{ name: 'pr-linter/exempt-test' }],
+        user: {
+          login: 'author',
+        },
+      };
+      const prLinter = configureMock(issue, undefined, ['Exemption Request: \nThe reason is blah blah blah.']);
+      await expect(prLinter.validatePullRequestTarget(SHA)).rejects.toThrow(
+        'The pull request linter fails with the following errors:' +
+        '\n\n\t❌ Fixes must contain a change to an integration test file and the resulting snapshot.' +
+        '\n\n<b>PRs must pass status checks before we can provide a meaningful review.</b>\n\n' +
+        'If you would like to request an exemption from the status checks or clarification on feedback,' +
+        ' please leave a comment on this PR containing `Exemption Request` and/or `Clarification Request`.' +
+        '\n\n✅ A exemption request has been requested. Please wait for a maintainer\'s review.',
+      );
+    });
+
+    test('valid exemption request with middle exemption request', async () => {
+      const issue: Subset<linter.GitHubPr> = {
+        number: 1,
+        title: 'fix: some title',
+        body: '',
+        labels: [{ name: 'pr-linter/exempt-test' }],
+        user: {
+          login: 'author',
+        },
+      };
+      const prLinter = configureMock(issue, undefined, ['Random content - Exemption Request - hello world']);
+      await expect(prLinter.validatePullRequestTarget(SHA)).rejects.toThrow(
+        'The pull request linter fails with the following errors:' +
+        '\n\n\t❌ Fixes must contain a change to an integration test file and the resulting snapshot.' +
+        '\n\n<b>PRs must pass status checks before we can provide a meaningful review.</b>\n\n' +
+        'If you would like to request an exemption from the status checks or clarification on feedback,' +
+        ' please leave a comment on this PR containing `Exemption Request` and/or `Clarification Request`.' +
+        '\n\n✅ A exemption request has been requested. Please wait for a maintainer\'s review.',
+      );
+    });
+  });
+
   describe('metadata file changed', () => {
     const files: linter.GitHubFile[] = [{
       filename: 'packages/aws-cdk-lib/region-info/build-tools/metadata.ts',
@@ -1074,7 +1139,7 @@ describe('integration tests required on features', () => {
   });
 });
 
-function configureMock(pr: Subset<linter.GitHubPr>, prFiles?: linter.GitHubFile[]): linter.PullRequestLinter {
+function configureMock(pr: Subset<linter.GitHubPr>, prFiles?: linter.GitHubFile[], existingComments?: string[]): linter.PullRequestLinter {
   const pullsClient = {
     get(_props: { _owner: string, _repo: string, _pull_number: number, _user: { _login: string} }) {
       return { data: pr };
@@ -1103,7 +1168,11 @@ function configureMock(pr: Subset<linter.GitHubPr>, prFiles?: linter.GitHubFile[
     deleteComment() {},
 
     listComments() {
-      return { data: [{ id: 1212121212, user: { login: 'aws-cdk-automation' }, body: 'The pull request linter fails with the following errors:' }] };
+      const data = [{ id: 1212121212, user: { login: 'aws-cdk-automation' }, body: 'The pull request linter fails with the following errors:' }];
+      if (existingComments) {
+        existingComments.forEach(comment => data.push({ id: 1212121211, user: { login: 'aws-cdk-automation' }, body: comment }));
+      }
+      return { data };
     },
 
     removeLabel: mockRemoveLabel,