Provide support for specifying the topic name

[tomkerkhove]

Is your feature request related to a problem? Please describe.
Users are forced to use entity-scoped namespaces, which is not always ideal.

Describe the solution you'd like
Provide support for specifying the topic name so that users can use namespace-scoped connection strings.

Describe alternatives you've considered
N/A

[stijnmoreels]

Ah, yes, that will be more in line with the other messaging stuff we have.