Improve datalayer Observability

[Mohamedma96]

There are existing TODOs in pkg/epp/datalayer/collector.go indicating missing support for collector-level metrics tracking. This issue is to track the design and implementation of metrics collection for collectors to improve observability and operational visibility.

Relevant TODOs:

• pkg/epp/datalayer/collector.go:77

  // TODO: optional metrics tracking collection (e.g., errors, invocations, ...)

• pkg/epp/datalayer/collector.go:115

  // TODO: track errors per collector?

Currently, collectors do not expose metrics such as invocation counts or error counts, which makes it difficult to monitor their behavior or diagnose failures in production environments.

The implementation should:

• Be optional and configurable

• Avoid introducing significant overhead when metrics collection is disabled