feat: Publish new fields to support cluster group routing for Cloud Bigtable (#928)

* feat: Publish new fields to support cluster group routing for Cloud Bigtable

Committer: @garye
PiperOrigin-RevId: 391576441

Source-Link: googleapis/googleapis@5f76113

Source-Link: googleapis/googleapis-gen@e01b342

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handwritten/bigtable/protos/google/bigtable/admin/v2/instance.proto

@@ -200,7 +200,11 @@ message AppProfile {
   // transient errors or delays. Clusters in a region are considered
   // equidistant. Choosing this option sacrifices read-your-writes consistency
   // to improve availability.
-  message MultiClusterRoutingUseAny {}
+  message MultiClusterRoutingUseAny {
+    // The set of clusters to route to. The order is ignored; clusters will be
+    // tried in order of distance. If left empty, all clusters are eligible.
+    repeated string cluster_ids = 1;
+  }
 
   // Unconditionally routes all read/write requests to a specific cluster.
   // This option preserves read-your-writes consistency but does not improve