ci: add GitHub Action to post welcome message on good first issues (#9707)

Co-authored-by: Engel Nyst <enyst@users.noreply.github.com>

.github/workflows/welcome-good-first-issue.yml

@@ -0,0 +1,50 @@
+name: Welcome Good First Issue
+
+on:
+  issues:
+    types: [labeled]
+
+permissions:
+  issues: write
+
+jobs:
+  comment-on-good-first-issue:
+    if: github.event.label.name == 'good first issue'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check if welcome comment already exists
+        id: check_comment
+        uses: actions/github-script@v7
+        with:
+          result-encoding: string
+          script: |
+            const issueNumber = context.issue.number;
+            const comments = await github.rest.issues.listComments({
+              ...context.repo,
+              issue_number: issueNumber
+            });
+
+            const alreadyCommented = comments.data.some(
+              (comment) =>
+                comment.body.includes('<!-- auto-comment:good-first-issue -->')
+            );
+
+            return alreadyCommented ? 'true' : 'false';
+
+      - name: Leave welcome comment
+        if: steps.check_comment.outputs.result == 'false'
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const repoUrl = `https://github.com/${context.repo.owner}/${context.repo.repo}`;
+
+            await github.rest.issues.createComment({
+              ...context.repo,
+              issue_number: context.issue.number,
+              body: "🙌 **Hey there, future contributor!** 🙌\n\n" +
+                    "This issue has been labeled as **good first issue**, which means it's a great place to get started with the OpenHands project.\n\n" +
+                    "If you're interested in working on it, feel free to! No need to ask for permission.\n\n" +
+                    "Be sure to check out our [development setup guide](" + repoUrl + "/blob/main/Development.md) to get your environment set up, and follow our [contribution guidelines](" + repoUrl + "/blob/main/CONTRIBUTING.md) when you're ready to submit a fix.\n\n" +
+                    "🙌 Happy hacking! 🙌\n\n" +
+                    "<!-- auto-comment:good-first-issue -->"
+            });