feat: Adds support for custom audiences

Custom Audiences
 * The new field is found in https://cloud.google.com/run/docs/reference/rest/v2/projects.locations.services.
 * For more information, see https://cloud.google.com/run/docs/configuring/custom-audiences.

PiperOrigin-RevId: 546032394

google/cloud/run/v2/service.proto

@@ -430,6 +430,13 @@ message Service {
   // Output only. The main URI in which this Service is serving traffic.
   string uri = 36 [(google.api.field_behavior) = OUTPUT_ONLY];
 
+  // One or more custom audiences that you want this service to support. Specify
+  // each custom audience as the full URL in a string. The custom audiences are
+  // encoded in the token and used to authenticate requests. For more
+  // information, see
+  // https://cloud.google.com/run/docs/configuring/custom-audiences.
+  repeated string custom_audiences = 37;
+
   // Output only. Reserved for future use.
   bool satisfies_pzs = 38 [(google.api.field_behavior) = OUTPUT_ONLY];