Implement keys endpoints to list access keys

[dodie]

Expected Behavior

Would it make sense to support the keys API?

For example, one can query the query access keys for repositories via the following URL:

https://<BITBUCKET_URL>/rest/keys/1.0/projects/<PROJECT>/repos/<REPO>/ssh

It would be really nice to have that in the client.

Context

My goal is to get an overview of authorization setup in my Bitbucket instance. I can already list project and repository permissions, but in addition to these, access keys can be directly configured for repositories to allow access to SSH keys.

If you consider this use-case valid, I'm happy to open a PR with the changes.

[cdancy]

@dodie absolutely! Any api that is not currently covered is worth putting in. Feel free to ping or ask questions if you need help with the PR.