chore: enforce major version for cdk, aws-cdk, and cli-lib-alpha (#352)

When a major version is defined, bumps will fail if the new version
crosses the major version boundary.

This makes sure that cdk, aws-cdk, and cli-lib-alpha bumps will always
be major version 2, or fail

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

Author: kaizencc

Diff for: .projenrc.ts

@@ -1242,6 +1242,7 @@ const cli = configureProject(
     nextVersionCommand: 'tsx ../../projenrc/next-version.ts maybeRc',
 
     releasableCommits: transitiveToolkitPackages('aws-cdk'),
+    majorVersion: 2,
   }),
 );
 
@@ -1378,6 +1379,7 @@ const cliLib = configureProject(
     disableTsconfig: true,
     nextVersionCommand: `tsx ../../../projenrc/next-version.ts copyVersion:../../../${cliPackageJson} append:-alpha.0`,
     releasableCommits: transitiveToolkitPackages('@aws-cdk/cli-lib-alpha'),
+    majorVersion: 2,
     eslintOptions: {
       dirs: ['lib'],
       ignorePatterns: [
@@ -1514,6 +1516,7 @@ const cdkAliasPackage = configureProject(
     deps: [cli.customizeReference({ versionType: 'exact' })],
     nextVersionCommand: `tsx ../../projenrc/next-version.ts copyVersion:../../${cliPackageJson}`,
     releasableCommits: transitiveToolkitPackages('cdk'),
+    majorVersion: 2,
     tsconfig: {
       compilerOptions: {
         ...defaultTsOptions,