Feat: Add Metrics Tracer and Metrics Tracer Factory

[jeremyprime]

Description

This PR introduces a metrics factory to the codebase. It's a direct follow-up to the previously merged metrics exporter (see PR #2272). This factory is responsible for creating and managing the specific service metrics that will be instrumented throughout the code in subsequent changes.

Impact

This change introduces new components but has no immediate impact as the factory is not called at this time.

Testing

Unit tests have been added to verify the correct functionality of the metrics factory and its interaction with the exporter. Additionally, manual verification confirmed that the factory and exporter correctly create and are capable of emitting metrics to Google Cloud Platform (GCP).

This PR introduces no breaking changes.

Additional Information

Future metrics work will involve:

• Developing a gRPC interceptor to capture and emit Google Front End (GFE) metrics.
• Integrating the created metrics into various parts of the codebase for actual instrumentation.

Checklist

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease
• Appropriate docs were updated
• Appropriate comments were added, particularly in complex areas or places that require background
• No new warnings or issues will be generated from this change

[lszinv]

Airlock failures are on:
npm error notarget No matching version found for @opentelemetry/resource-detector-gcp@^0.33.0.

https://www.npmjs.com/package/@opentelemetry/resource-detector-gcp/v/0.33.0?activeTab=versions
0.33 seems to have been available since 4 months ago though.

[jeremyprime]

Should the service metrics and GFE metrics be enabled or disabled by default? And what should the env vars be?

In Java I see:

SPANNER_DISABLE_BUILTIN_METRICS
SPANNER_DISABLE_DIRECT_ACCESS_GRPC_BUILTIN_METRICS

Which sounds like they should be enabled by default and the env vars can be set to turn them off.

[jeremyprime]

Note that these metric attributes can be determined at construction time, but the projectid, instanceid, and databaseid are not available during client construction (when this factory will be created), which is why they are not set here. I copied equivalent methods to create the clientuid and clienthash, and detect location, from other clients.