Add size GH workflow (#198)

Author: afritzler

.github/workflows/size-label.yml

@@ -0,0 +1,20 @@
+name: Size Label
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - edited
+      - synchronize
+
+jobs:
+  size-label:
+    permissions:
+      contents: read
+      pull-requests: write
+    runs-on: ubuntu-latest
+    steps:
+      - name: size-label
+        uses: pascalgn/[email protected]
+        env:
+          GITHUB_TOKEN: "${{ secrets.GITHUB_TOKEN }}"