Auto assign PR to author (#16969)

I think most PRs remain unassigned, so this PR auto assigns the PR to the PR author. I think this will help keep our project boards up-to-date.

Authors:
  - Matthew Murray (https://github.com/Matt711)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)

URL: #16969

.github/workflows/auto-assign.yml

@@ -0,0 +1,17 @@
+name: "Auto Assign PR"
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - reopened
+      - synchronize
+
+jobs:
+  add_assignees:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions-ecosystem/action-add-assignees@v1
+        with:
+          repo_token: "${{ secrets.GITHUB_TOKEN }}"
+          assignees: ${{ github.actor }}

.github/workflows/labeler.yml

@@ -1,4 +1,5 @@
 name: "Pull Request Labeler"
+
 on:
 - pull_request_target