Default IntegrationProfile

### Requirement

We should consider that any Integration can use, by default, an IntegrationProfile named "default" if it exists in its same namespace or the same namespace annotated with the default to use. In this way we can let the admin to provide a specific default profile in each namespace and avoid to request the user to annotate the integrations explicitly.

Start by tracing how Integrations currently resolve their IntegrationProfile and how namespace annotations are read. Check the existing Integration and IntegrationProfile behavior before deciding how same-namespace and annotated namespace defaults should be prioritized. Done means an Integration can use the appropriate default profile without an explicit annotation, with behavior covered for both namespace cases.

Written by the indexing model from the issue text.