Add AggregatedMetrics to support multiple Metrics implementations

[Donnerbart]

Partially fixes #2884
Alternative to #2912

See #2912 (comment)

[Copilot]

Pull Request Overview

This PR introduces an AggregatedMetrics class that implements the composite pattern to aggregate multiple Metrics implementations, allowing simultaneous collection of metrics data by different monitoring systems.

Key changes:

• New AggregatedMetrics class that delegates calls to multiple metrics instances
• Special handling for timeControllerExecution() which only delegates to the first metrics instance
• Comprehensive test suite with 100% coverage of the new functionality

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
AggregatedMetrics.java	Core implementation of the composite metrics aggregator with delegation logic
AggregatedMetricsTest.java	Complete test suite covering constructor validation, method delegation, and special cases
pom.xml	Added mockito-core test dependency for unit testing

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Donnerbart]

The new class should probably go into the same package as the Metrics interface. It has nothing to do with the concrete MicroMeter implementation. Will update the PR tomorrow.

[metacosm]

Good point. I forgot about that when I suggested this design! 😓

[xstefank]

LGTM

[csviri]

Hi @Donnerbart loogks, great, would be better if you could target next branch, for the next minor version. Maybe also to mention this addon on docs (here https://javaoperatorsdk.io/docs/documentation/observability/ ). otherwise great, thank you

[Donnerbart]

• Moved the class into the io.javaoperatorsdk.operator.api.monitoring package.
• Changed the target branch to next.
• Added and improved the documentation.