Add GH action to manage servicing branch codeflow. (dotnet#18267)

Author: JoeRobich

.config/feature-lsp-branch-merge.json

@@ -0,0 +1,8 @@
+{
+    "merge-flow-configurations": {
+        "main": {
+            "MergeToBranch": "feature/lsp",
+            "ExtraSwitches": "-QuietComments"
+        }
+    }
+}

.config/service-branch-merge.json

@@ -0,0 +1,13 @@
+{
+    "merge-flow-configurations": {
+        // regular branch flow
+        "release/dev17.13": {
+            "MergeToBranch": "main",
+            "ExtraSwitches": "-QuietComments"
+        },
+        "main": {
+            "MergeToBranch": "release/dev17.14",
+            "ExtraSwitches": "-QuietComments"
+        }
+    }
+}

.github/workflows/branch-merge.yml

@@ -0,0 +1,22 @@
+# Merges any changes from servicing branches forward.
+
+name: Flow servicing changes to main
+on:
+  push:
+   branches:
+     - 'release/*'
+     - 'main'
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  servicing-flow:
+    uses: dotnet/arcade/.github/workflows/inter-branch-merge-base.yml@main
+    with:
+      configuration_file_path: '.config/service-branch-merge.json'
+  feature-lsp-flow:
+    uses: dotnet/arcade/.github/workflows/inter-branch-merge-base.yml@main
+    with:
+      configuration_file_path: '.config/feature-lsp-branch-merge.json'