add repo settings for grpc-experimental

Author: cindy-peng

.github/sync-repo-settings.yaml

@@ -203,6 +203,23 @@ branchProtectionRules:
       - 'Kokoro - Test: Java GraalVM Native Image'
       - 'Kokoro - Test: Java 17 GraalVM Native Image'
       - javadoc
+  - pattern: grpc-experimental
+    isAdminEnforced: true
+    requiredApprovingReviewCount: 1
+    requiresCodeOwnerReviews: true
+    requiresStrictStatusChecks: false
+    requiredStatusCheckContexts:
+      - dependencies (17)
+      - lint
+      - clirr
+      - units (8)
+      - units (11)
+      - 'Kokoro - Test: Integration'
+      - cla/google
+      - OwlBot Post Processor
+      - 'Kokoro - Test: Java GraalVM Native Image'
+      - 'Kokoro - Test: Java 17 GraalVM Native Image'
+      - javadoc
 permissionRules:
   - team: yoshi-admins
     permission: admin