chore: setup 2.39.x lts branch (#2302)

Author: zhumin8

.github/release-please.yml

@@ -58,5 +58,12 @@ branches:
       - >-
         google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/Version.java
     branch: 2.30.x
+  - bumpMinorPreMajor: true
+    handleGHRelease: true
+    releaseType: java-backport
+    extraFiles:
+      - >-
+        google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/Version.java
+    branch: 2.39.x
 extraFiles:
   - google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/Version.java

.github/sync-repo-settings.yaml

@@ -142,6 +142,24 @@ branchProtectionRules:
       - 'Kokoro - Test: Java 17 GraalVM Native Image'
       - javadoc
       - conformance
+  - pattern: 2.39.x
+    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
+      - conformance
 permissionRules:
   - team: yoshi-admins
     permission: admin