Workflow: Add label "staff" to issues and PR to help prioritisation (#4726)

* Create add_staff_label.yml

* print context

* 2 steps for different types

* set GH_TOKEN at job level

* clean up a little

* Update add_staff_label.yml

* is this the syntax?

* run only when PR is opened, not synchronised

* Apply suggestion from @joshblack

Co-authored-by: Josh Black <[email protected]>

---------

Co-authored-by: Josh Black <[email protected]>

Author: siddharthkp

.github/workflows/add_staff_label.yml

@@ -0,0 +1,23 @@
+name: Add Staff Label
+
+on:
+  issues:
+    types: [opened, reopened]
+  pull_request:
+    types: [opened, reopened]
+
+jobs:
+  add-staff-label:
+    if: ${{ github.repository == 'primer/react' }}
+    runs-on: ubuntu-latest
+    env:
+      GH_TOKEN: ${{ github.token }}
+    steps:
+      - name: Add label to issue
+        if: ${{ github.event.issue.author_association == 'MEMBER' }}
+        run: |
+          gh issue edit ${{github.event.issue.html_url}} --add-label staff
+      - name: Add label to pull_request
+        if: ${{ github.event.pull_request.author_association == 'MEMBER' }}
+        run: |
+          gh pr edit ${{github.event.pull_request.html_url}} --add-label staff