refactor(platform/bitbucket-server): split initRepo (#14606)

* Move getting repo git url logic into a function similar to gitlab implementation as per request in another PR:
https://github.com/renovatebot/renovate/pull/13875#issuecomment-1023980178



* Bitbucket server - Move getRepoGitUrl into utils

Co-authored-by: Rhys Arkins <rhys@arkins.net>
Co-authored-by: Michael Kriese <michael.kriese@visualon.de>