add action to welcome new users

Author: eschutho

.github/workflows/welcome-new-users.yml

@@ -0,0 +1,25 @@
+name: Welcome New Contributor
+
+on:
+  pull_request_target:
+    types: [opened]
+
+jobs:
+  welcome:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+
+    steps:
+      - name: Welcome Message
+        uses: actions/[email protected]
+        with:
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          pr-messsage: |-
+            Congrats on making your first PR and thank you for contributing to Superset! :tada: :heart:
+            We hope to see you in our [Slack](https://apache-superset.slack.com/) community too!
+      - name: First Time Label
+        uses: andymckay/labeler@master
+        with:
+          add-labels: "new:contributor"
+          repo-token: ${{ secrets.GITHUB_TOKEN }}