Add workflow for automatic SDK updates

Copy of dotnet/extensions#4886

Author: RussKie

.github/workflows/update-sdk.yml

@@ -0,0 +1,28 @@
+name: update-dotnet-sdk
+
+on:
+
+  # Scheduled trigger to check for .NET SDK updates at 12 UTC every Monday
+  schedule:
+    - cron:  '00 12 * * MON'
+
+  # Manual trigger to update the .NET SDK on-demand.
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  issues: write
+  pull-requests: write
+
+jobs:
+  update-dotnet-sdk:
+    name: Update .NET SDK
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        ref: dev
+    - uses: martincostello/update-dotnet-sdk@65c5f402b15326dd12d7b1dac63abdbb53ed695c # v3.1.2
+      with:
+        quality: 'daily'
+        repo-token: ${{ secrets.GITHUB_TOKEN }}