Add an Actions workflow to prompt folks to update the docs changelog (#57067)

Co-authored-by: Copilot <[email protected]>

Author: hubwriter

.github/workflows/changelog-prompt.yml

@@ -0,0 +1,66 @@
+name: Changelog prompt when a PR is closed
+
+on:
+  pull_request:
+    types: [closed]
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  comment-on-pr:
+    # This workflow should only run on the 'github/docs-internal' repository because it posts changelog instructions
+    # and links that are specific to the internal documentation process and resources.
+    # It also only runs if PR is merged into the main branch.
+    if: github.repository == 'github/docs-internal' && github.event.pull_request.merged == true && github.event.pull_request.base.ref == 'main'
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check if PR author is in docs-content team
+        id: check_team
+        uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
+        with:
+          github-token: ${{ secrets.DOCS_BOT_PAT_BASE }}
+          script: |
+            try {
+              const pr = context.payload.pull_request;
+              await github.rest.teams.getMembershipForUserInOrg({
+                org: 'github',
+                team_slug: 'docs-content',
+                username: pr.user.login,
+              });
+              core.exportVariable('CONTINUE_WORKFLOW', 'true');
+            } catch(err) {
+              core.info("Workflow triggered by a merged PR, but the PR author is not a member of the docs-content team.");
+              core.exportVariable('CONTINUE_WORKFLOW', 'false');
+            }
+
+      - name: Post changelog instructions comment
+
+        if: env.CONTINUE_WORKFLOW == 'true'
+
+        uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
+        with:
+          github-token: ${{ secrets.DOCS_BOT_PAT_BASE }}
+          script: |
+            // Get PR author username
+            const pr = context.payload.pull_request;
+            const prAuthor = pr.user.login;
+
+            // Compose the comment body with readable YAML and correct formatting
+            const commentBody =
+              "👋 @" + prAuthor +
+              " - Did this PR add noteworthy changes to the GitHub docs? If so, you might want to publicize this by adding an entry to " +
+              "the [Docs changelog](https://github.com/github/docs-internal/blob/main/CHANGELOG.md).\n\n" +
+              "To do this, type `/changelog` in a new comment on this PR and complete the fields.\n\n" +
+              "A message will be posted to the **#docs-changelog** channel and a PR will be raised to update the [CHANGELOG.md](/CHANGELOG.md) file.";
+
+            // Post the comment
+            await github.rest.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: pr.number,
+              body: commentBody
+            });