chore: add instructions to enable builtin metrics (googleapis#1358)

* chore: add instructions to enable builtin metrics

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

.readme-partials.yml

@@ -115,6 +115,19 @@ custom_content: |
 
   TIP: If you are experiencing version conflicts with gRPC, see [Version Conflicts](#version-conflicts).
 
+  ## Enabling client side metrics
+  
+  Cloud Bigtable client supports publishing client side metrics to
+  [Cloud Monitoring](https://cloud.google.com/monitoring/docs/monitoring-overview) under the
+  `bigtable.googleapis.com/client` namespace.
+  
+  Please fill out this [Google Form](https://forms.gle/xuhu6vCunn2MjV2m9) to sign up for the private preview of this
+  feature. And enable it by setting:
+  
+  ```java
+  BigtableDataSettings.enableBuiltinMetrics();
+  ```
+    
   ## Client request tracing: OpenCensus Tracing
 
   Cloud Bigtable client supports [OpenCensus Tracing](https://opencensus.io/tracing/),

README.md

@@ -213,6 +213,19 @@ try {
 
 TIP: If you are experiencing version conflicts with gRPC, see [Version Conflicts](#version-conflicts).
 
+## Enabling client side metrics
+
+Cloud Bigtable client supports publishing client side metrics to
+[Cloud Monitoring](https://cloud.google.com/monitoring/docs/monitoring-overview) under the
+`bigtable.googleapis.com/client` namespace.
+
+Please fill out this [Google Form](https://forms.gle/xuhu6vCunn2MjV2m9) to sign up for the private preview of this
+feature. And enable it by setting:
+
+```java
+BigtableDataSettings.enableBuiltinMetrics();
+```
+
 ## Client request tracing: OpenCensus Tracing
 
 Cloud Bigtable client supports [OpenCensus Tracing](https://opencensus.io/tracing/),