IssueTracker

This will create a feature request which anybody can view and comment on.

Please describe your requested enhancement. Good feature requests will solve common problems or enable new use cases.

What you would like to accomplish:
- Use Telemetry to get the client-side metrics of a Spanner instance, for example the session pool status[1].

How this might work:
- Migrate the OpenCensus instrumentation about Spanner client library to OpenTelemetry.

If applicable, reasons why alternative solutions are not sufficient:
- OpenCensus has become deprecated since July 2023[2] and it will have limited support and maintenance in the future.

Other information (workarounds you have tried, documentation consulted, etc):
- The users can use OT bridge to convert OpenCensus metrics to OpenTelemetry[3], however it would be better to get OpenTelemetry metrics directly.

[1] https://cloud.google.com/blog/products/spanner/troubleshooting-cloud-spanner-applications-with-opencensus-metrics
[2] https://opentelemetry.io/blog/2023/sunsetting-opencensus/#what-to-expect-after-july-31-2023
[3] https://opentelemetry.io/blog/2023/sunsetting-opencensus/#how-to-migrate-to-opentelemetry