chore: Refactor getAuthProvider out of vscode-bootstrap

Issue: #345 (closed)

Description

• This helps support uninstalling extensions since we'd like to do this out of the vscode-bootstrap class and we need to make a GitLab request.
• !314 (comment 1909367059)

Screenshots

Nothing should change but everything should still work 😄

☝ The token refreshing helps confirm that we're setting up our client and other AuthProvider decorators correctly 👍