Add per db metrics

[benjaminjb]

Checklist:

• Have you added an explanation of what your changes do and why you'd like them to be included?
• Have you updated or added documentation for the change, as applicable?
• Have you tested your changes on all related environments with successful results, as applicable?
  • Have you added automated tests?

Type of Changes:

• New feature
• Bug fix
• Documentation
• Testing enhancement
• Other

What is the current behavior (link to any open issues here)?

No per-db metrics

What is the new behavior (if this is a feature change)?

• Breaking change (fix or feature that would cause existing functionality to change)

• Add per-db metrics (based on pgMonitor v5.2.1)

• Allow per-db custom metrics

Other Information:
Issues: [PGO-21]

[benjaminjb]

Some notes on this PR:

• I based the per db metrics on pgmonitor 5.2.1, which Drew is bumping to elsewhere
• some per db metrics were already included in internal/collector/gte_pg16_slow_metrics.yaml/internal/collector/lt_pg16_slow_metrics.yaml, so I moved them over to the per db metric list; this let me delete those files and update some of the logic for adding metrics
• I added steps to our OTel KUTTL test (beginning to strain at the bounds of a reasonable test, might break up in the future) to test the different functionality added: targeting certain dbs with the defaults; removing metrics from the defaults; adding custom per db metrics.

[cbandy]

🤔 IIUC, this and customQueries only make sense at/on Postgres. Is there a way to arrange structs so the PGAdmin API doesn't have these fields? Not a blocker; v1beta1.

[benjaminjb]

I didn't want to make any too big changes with the spec, but I wonder if the pgadmin and postgrescluster versions will diverge even more (or if we'll eventually want to slice up instrumentation by target-type, eg., postgres-instrumentation, pgbouncer-instrumentation, pgadmin-instrumentation).

[dsessler7]

Hmm yeah good point... Probably makes sense to at least have a pgadmin-instrumentation and a postgrescluster-instrumentation and then pick and choose which structs make sense in each