[Feature] Support BitBucket data center

[Kennybll]

Currently t3code only supports BitBucket Cloud. I am trying to use t3code at work, but we use BitBucket data center so the BitBucket integration does not work since it uses different endpoints.

[iOSDeveloperGuy]

+1 for this. We use a self-hosted Bitbucket Data Center instance on a custom internal domain, so this is currently the main thing keeping us from being able to use the Bitbucket integration fully.

For us, the most useful initial scope would be authenticating against a custom Data Center instance and supporting the normal PR workflow: create/view PRs, diffs, comments, reviewers, and merge/decline.

I'd also be happy to help test this against a real Data Center instance, or help with the implementation if that's useful.