CLDR-17181 add auto author assign

- whoever opens the PR, gets assigned to it by default.
- can reassign if needed.

.github/workflows/auto-author-assign.yml

@@ -0,0 +1,15 @@
+# .github/workflows/auto-author-assign.yml
+name: Auto Author Assign
+
+on:
+  pull_request_target:
+    types: [ opened, reopened ]
+
+permissions:
+  pull-requests: write
+
+jobs:
+  assign-author:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: toshimaru/[email protected]