Provide better observability into RU consumption

This issue tracks surfacing how many RUs are consumed for a workload running on CockroachDB serverless. This will help serverless developers and operators forecast costs and understand RU consumption relative to their application workload.

Touch points include:

1. Like rowCount, RU consumed is returned as part of the result for each statement execution (real-time feedback on how expensive running a statement is)
2. RU consumed is surfaced as part of crdb_internal.statement_statistics, crdb_internal. statement_statistics, and execution_insights (historical troubelshooting).

Note: We must determine if RUs should be hidden for Dedicated/Self-hosted. Especially in crdb_internal and programmatic touch points.

Jira issue: CRDB-24103

Epic CRDB-32139