Allow to exclude namespaces nestead namespaces

[ghostbuster91]

When generating scala classes from smithy model we often need to exclude certain namespaces due to various reasons.

For that we were using --exclude-ns option in smithy4s-cli. However, recently we did some small refactoring that moved some of the shapes from the top namespace that was excluded (e.g. a.b) into sub-namespaces (e.g. a.b.c and a.b.d).

This cause issues in the generated code as those nested namespaces were not excluded.

Would it be possible to allow excluding namespaces in a more convenient way? e.g. --exclude-ns a.b.* would exclude .a.b as well as any other namespace that starts with a.b

[kubukoz]

I'm all for it, if it's simple to implement then it shouldn't be a big deal to @Baccata either I assume

[Baccata]

PR away :)