Support for Bitbucket Server

[KatharinaSick]

Hi,

since Bitbucket Server now (finally) supports OAuth2, it would be great to add support for it to this strategy as well. I already tried if this strategy works with Bitbucket Server and everything until parsing the user profile succeeds. Parsing the user profile unfortunately fails, because Bitbucket Server has a different user profile response format than Bitbucket Cloud (docs).

This means, we could add support for Bitbucket Server by editing the profile.js. Would you be open for a contribution from my side?
My plan would be to add a boolean flag to the strategy whether one is authenticating against Bitbucket Server (false by default) and if set, the profile would get parsed differently.

[KatharinaSick]

@gtanner @tqc would you accept a PR that adds Bitbucket Server support?

Sorry for pinging you directly, but I would really like to solve this with a PR rather than a new strategy that is forked from yours.