Explicit export

[bartoszmajsak]

Allow users to explicitly define specific services for export by listing them in a format as <namespace>/<service>.

This gives the admin full control over exported services.

Example structure

serviceList:
  - "ns-1/ratings"
  - "ns-1/reviews"
  - "ns-2/*"

[bartoszmajsak]

Similar to #144, we should carefully consider the exact use cases. One aspect that isn't clear to me is how we should handle cases where e.g. ns-2 is not part of the mesh. It's important to explicitly define this behavior and document it accordingly.

I think the general assumption is that we only consider namespaces which are part of the mesh, but we need to be clear on it to avoid ambiguity.