Implementations of the missing RepositoriesClient methods

There are some concerns regarding naming here to be aware of. Specifically the response model `RepositoryTag`. A class named `GitTag` already exists but the structures are quite different. It looks as if this might be more in line with a lightweight tag so `LightweightTag` might do as a name instead.

Secondly the builder implementation in the integration tests is silly at this point, but it felt even sillier repeating the longer section over and over. And this way the option to change the defaults is more centralized and it's easy to add methods to the builder for more customization if it's ever needed. I can take it or leave it but if it stays I have another commit that replaces the hardcoded instantiations throughout the integration tests.

Hopefully there aren't many other issues :)