Add scheduled merges to feature branch

Author: dibarbet

.github/workflows/scheduled-branch-merge.yml

@@ -0,0 +1,25 @@
+# See https://github.com/dotnet/arcade/blob/e52018a/Documentation/Maestro/New-Inter-Branch-Merge-Approach.md
+
+name: Scheduled branch merge
+on:
+  schedule:
+    # Create a merge every day (works only for merges from `main`, others would need a `push` trigger).
+    - cron: '0 0 * * *'
+  workflow_dispatch:
+    inputs:
+      configuration_file_branch:
+        description: 'Branch to use for configuration file'
+        required: true
+        default: 'main'
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  merge:
+    if: github.repository == 'dotnet/roslyn'
+    uses: dotnet/arcade/.github/workflows/inter-branch-merge-base.yml@main
+    with:
+      configuration_file_path: 'eng/config/community-to-main-branch-merge.jsonc'
+      configuration_file_branch: ${{ inputs.configuration_file_branch || 'main' }}

eng/config/feature-branch-merge.jsonc

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+// Used by .github/workflows/scheduled-branch-merge.yml
+{
+    "merge-flow-configurations": {
+        // Merge main into feature branches
+        "main": {
+            "MergeToBranch": "features/collection-expression-arguments",
+            // ExtraSwitches is an optional parameter which is accepted by the script: https://github.com/dotnet/arcade/blob/main/.github/workflows/inter-branch-merge-base.yml.
+            "ExtraSwitches": "-QuietComments"
+        }
+    }
+}