Introduce topic name field to create topic with underscores

[eshepelyuk]

Hello

Currently topic name is picked up from Topic resource.
Because k8s has limitations for resource names - there's no possibility to create topics named like simple_topic.

[dmacrei]

I have the same issue and I'd like to add this in.

[eshepelyuk]

This task is redundant, because the desired behaviour can be achieved by adding annotation to Topic resource.

crossplane.io/external-name: "simple_topic"