Add GitHub action to assign reviewers on PR created by Dependabot (#285)

Author: jnmt

.github/workflows/assign-dependabot-pr-reviewers.yaml

@@ -0,0 +1,19 @@
+name: Assign reviewer to dependabot PRs
+# This action assigns the ScalarDL team as reviewers when Dependabot opens a pull request.
+
+on:
+  pull_request:
+    types: [opened]
+
+jobs:
+  assign-reviewer:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+
+    steps:
+      - name: Assign ScalarDL team as reviewers for Dependabot PRs
+        env:
+          GH_TOKEN: ${{ secrets.ASSIGN_PR_REVIEWERS_PAT }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+          REPOSITORY: ${{ github.repository }}
+        run: gh pr edit $PR_NUMBER --repo $REPOSITORY --add-reviewer scalar-labs/scalardl