Allow declarative configuration of the default user quotas

[scholzj]

Kafka allows to configure default user quotas which apply to all users who do not have a specific quota setting. But they can be configured only dynamically using the Kafka Admin APi / kafka-config.sh. It might be useful to be able to configure them declaratively in the Kafka CR.

Open points:

• Should we also allow declarative configuration of the default client quota? We currently don't support declarative management of client quotas at all. So probably not

Also, the #9096 should be fixed first.

[scholzj]

Triaged in the community call on 21.9.2023: This makes sense. But it will need API changes, so it should have a proposal.

[scholzj]

The design was approved in StrimziProposal#68. This can be now implemented according to the proposal.