Add automatic DCO Check failure notification action.

The check itself comes from the DCO Check GitHub app. These apps are
tied directly to GitHub which is why the `app_id` is a known constant.
It's the same id regardless of the repository it monitors.

These were forked from MLFlow's public repository:

https: //github.com/mlflow/mlflow/blob/master/.github/workflows/notify-dco-failure.js
Signed-off-by: Jesse Whitehouse <[email protected]>

Author: susodapop

.github/workflows/notify-dco-failure.js

@@ -0,0 +1,49 @@
+module.exports = async ({ context, github }) => {
+    const { owner, repo } = context.repo;
+    const { number: issue_number } = context.issue;
+    const ref = context.payload.pull_request.head.sha;
+    const { user } = context.payload.pull_request;
+  
+    function sleep(ms) {
+      return new Promise(resolve => setTimeout(resolve, ms));
+    }
+  
+    async function getDcoCheck() {
+      const backoffs = [0, 2, 4, 6, 8];
+      const numAttempts = backoffs.length;
+      for (const [index, backoff] of backoffs.entries()) {
+        await sleep(backoff * 1000);
+        const resp = await github.checks.listForRef({
+          owner,
+          repo,
+          ref,
+          app_id: 1861, // ID of the DCO check app
+        });
+  
+        const { check_runs } = resp.data;
+        if (check_runs.length > 0 && check_runs[0].status === "completed") {
+          return check_runs[0];
+        }
+        console.log(
+          `[Attempt ${index + 1}/${numAttempts}]`,
+          "The DCO check hasn't completed yet."
+        );
+      }
+    }
+  
+    const dcoCheck = await getDcoCheck();
+    if (dcoCheck.conclusion !== "success") {
+      const body = [
+        `@${user.login} Thanks for the contribution! The DCO check failed. `,
+        `Please sign off your commits by following the instructions here: ${dcoCheck.html_url}. `,
+        "See https://github.com/databricks/databricks-sql-python/blob/main/CONTRIBUTING.md#sign-your-work for more ",
+        "details.",
+      ].join("");
+      await github.issues.createComment({
+        owner,
+        repo,
+        issue_number,
+        body,
+      });
+    }
+  };

.github/workflows/notify-dco-failure.yml

@@ -0,0 +1,21 @@
+name: Notify DCO Failure
+
+on:
+  pull_request_target:
+    types:
+      - opened
+
+jobs:
+  notify:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          submodules: recursive
+      - uses: actions/github-script@v4
+        with:
+          script: |
+            const script = require(
+              `${process.env.GITHUB_WORKSPACE}/.github/workflows/notify-dco-failure.js`
+            );
+            script({ context, github });