Add ApiOptions overloads to methods on I(Observable)RepositoryDeployKeysClient

[alexander-efremov]

Refer #1175 .

To-do:

• Add overload Task> GetAll(ApiOptions options) on IRepositoryDeployKeysClient.
• Add overload IObservable GetAll(ApiOptions options) on IObservableRepositoryDeployKeysClient.
• Add unit tests for these new methods.
• Add integration tests for these new methods.
  I've implemented the integration tests, but they are skipped now, because we don't have opportunity generate ssh keys in C# code (Review CanRetrieveAllDeployKeys test #1003).
  Also I haven't implemented integration tests for ObservableRepositoryDeployKeysClient because internally ObservableRepositoryDeployKeysClient use RepositoryDeployKeysClient that have integration tests already (just they skipped 😄 ).

/cc @shiftkey , @ryangribble

[alexander-efremov]

@shiftkey, @ryangribble please review these PR whenever possible, it's done.

[shiftkey]

@dampir 👍