Option to authenticate against BitBucket server w/ `git-credential`

## Problem

My company is building a managed remote coding environment (a bit like GitHub Codespaces) where code is being pulled from repos in a handful of different enterprise BitBucket Server instances. We would like to use this plugin to allow in-editor interaction w/ BitBucket, notably creating and interacting with PRs. There isn't any Jira offering that needs to be connected.

We've customized the auth of our BitBucket Server instances to support something more token based. On the coding environment side, we register a git credential provider provides short-lived credentials that we use both for HTTPS based git interactions and to interact with the BitBucket REST API. **Unfortunately, I don't think there's any way to use this with the atlascode VS code plugin.**

## Possible solution

Ideally there would be some way (hidden behind some setting is fine) to have the BitBucket HTTP clients fallback to using basic auth obtained by calling out to `git credential fill`.

## Describe alternatives you've considered

There is something technically achievable w/ a PAT, but creating & storing these long-lived access tokens as well as asking users to copy-paste them is unacceptable for us from a security standpoint.