Enhance the metrics experience for CockroachDB Serverless

A first-class observability experience starts with having the appropriate high-level signals and metrics for users to troubleshoot and tune their database(s). This epic tracks enhancing the metrics experience for CockroachDB Serverless which include:

- Removing irrelevant metrics in the Custom Metric experience that are not actionable (TBD: @Kevin Ngo to pull from essential metrics list)
- Additional Slack context: https://cockroachlabs.slack.com/archives/C02P01CDKKP/p1675296337926839 - Connect your Slack account
- Adding telemetry data to the Custom Metric experience so that we can track commonly configured metric charts
- Add essential metrics missing for the CockroachDB Serverless experience
- We can start narrowing down this list: https://docs.google.com/spreadsheets/d/1NaNHdD1csGtCHBS3Cd1Fr_Tk3SuRY7AQcO0x_V12uSM/edit#gid=31101091
- Bring metrics to Dedicated to have parity with Serverless
- Note more metrics could be relevant to Dedicated but we ill file a separate tracking issue for this


Jira issue: CRDB-29515

Epic CRDB-32130