Add proposal for integrating Bridge with Metrics Reporter

[fvaleri]

Add proposal for integrating Bridge with Metrics Reporter.

[fvaleri]

@ppatierno thanks for the review. I reworked the proposal to always present the Bridge changes first, and addressed the other comments.

[ppatierno]

This section is about the integration within the Cluster Operator which will be in charge of creating the application.properties file for the bridge but what about when the bridge runs as standalone on bare metal or VMs. In order to use the Strimzi metrics reporter, the user would need to set other parameters like disabling the JMX reporter (auto.include.jmx.reporter=false), disabling the Prometheus listener to avoid clashing with the port 8080 used by the bridge itself (prometheus.metrics.reporter.listener.enable=false).
It would be a bridge documentation update but I would mention the needed configuration here as well, maybe having a dedicated section for standalone bridge.

[fvaleri]

There is an example in "Metrics configuration types" paragraph, but I will improve it. For auto.include.jmx.reporter there is no mention in the Strimzi Metrics Reporter proposal, so we will leave that to the user. Additionally, that property will be removed in Kafka 4.0, and the user would need to explicitly add the JMX metrics plugin when setting any other custom plugin (See #11019).

[ppatierno]

But we could end in a Strimzi version with Kafka 3.9 support, so the auto.include.jmx.reporter would be still needed, or?

[fvaleri]

Given it's deprecated and not required to enable the Strimzi Metrics Reporter, I would leave this configuration to the user through .spec.kafka.config. Wdyt?

[PaulRMellor]

The overall approach makes sense.
I left a few suggestions, including a couple of questions where I wasn't clear on parts of the proposal.