Instrument query execution with Micrometer Observations

[zantvoort]

Storm already ships Spring Boot integration; the 1.13.0 milestone tightens it further. This issue covers observability.

There is currently no metrics or tracing support. A generic DataSource proxy can time statements, but Storm knows the repository, entity and operation behind every statement it generates, so it can emit far better-tagged signals. Instrumenting through Micrometer's Observation API yields actuator metrics and tracing spans from a single instrumentation.

Tasks:

• Query execution observer hook in core (instance-scoped, see Make framework integration points instance-scoped #198)
• Micrometer binding, auto-configured when an ObservationRegistry bean is present
• Tags: entity/projection, repository, operation; no raw SQL or parameter values in high-cardinality tags
• Docs