Authenticate with custom endpoint over websockets

[alanpog]

Same motivation as #278, but using websockets instead. It was confusing that I could manually supply an endpoint using rest and it would be ignored if going over sockets.

This PR aims to do for websockets what #278 did for the rest provider, i.e., to allow the client to authenticate with a custom endpoint such as auth/facebook.

[alanpog]

Is this PR made obsolete by #336 ?

[ekryski]

Yeah but I wanted to get the docs and the client in order before I closed it so that I could explain why and how you can do what you want to do 😄

[alanpog]

So let's keep this open as a reminder then, I'll be very grateful to be explained how to do this in 1.0. Thanks.

[ekryski]

We haven't created a guide for it so would gladly take a PR to the docs for one, but you can easily change up the default path/endpoint on any of the authentication plugins that support it. All of the options are outlined in the docs.

For example, for OAuth2: https://docs.feathersjs.com/api/authentication/oauth2.html#default-options