Fix #2687: Allow multiple integration platforms in the same namespace

[nicolaferraro]

This (together with #2683) enables the upgrade/downgrade of individual integrations, handing them off to two different operators concurrently running in the same namespace. I've created a POC here: https://github.com/nicolaferraro/camel-k-selective-upgrade-demo

I've changed a bit #2683, to use an annotation for the operator.id instead of a label (and added a sibling platform.id annotation), since we're not using label selectors to query for them.

So we have two annotations that can be applied to any Camel K resource:

• camel.apache.org/operator.id: allows to specify the operator that should reconcile the resource
• camel.apache.org/platform.id: allows to specify the platform that should be used as global configuration

And another annotation that can be applied on a platform (camel.apache.org/secondary.platform) that can mark a platform as secondary to prevent the controller to mark it as "Duplicate" and allow using it explicitly.

Done:

• Feature
• E2E Tests
• Documentation

Release Note

Resources can be configured to use a secondary integration platform