feat: support self-hosted git repositories

[Almighty-Alpaca]

Description

This PR implements support for self-hosted git repositories. This configuration syntax for this is as follows:

repository:
  type: gitlab
  origin: https://gitlab.example.dev
  owner: invertase
  name: melos

I initially tried to use RegEx to extract this information from only the URL, but GitLab supports both subgroups and hosting not on the root of a domain. This means that https://example.com/gitlab/invertase/melos could be both a GitLab instance on https://example.com/gitlab with a group named invertase or an instance on https://example.com/ with a group/subgroup of gitlab/invertase. I was also tempted to validate the owner/name fields using RegEx, but at least for GitLab the patterns are unnecessary complicated and use features that aren't available in Dart.

I've also gone ahead and mirrored the syntax for GitHub, but since I lack knowledge of GitHub Enterprise as much as access to an instance of it this is currently untested. I'd appreciate if anyone here has the resources to help out with this.

Closes #392

Type of Change

• ✨ feat -- New feature (non-breaking change which adds functionality)
• 🛠️ fix -- Bug fix (non-breaking change which fixes an issue)
• ❌ ! -- Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 refactor -- Code refactor
• ✅ ci -- Build configuration change
• 📝 docs -- Documentation
• 🗑️ chore -- Chore

[blaugold]

Very nice! Just some minor issues.

[Almighty-Alpaca]

Very nice! Just some minor issues.

Should be all fixed now