feat: Add GitLab authentication feature.

[ev-gor]

Vanguard PR

Description

Authentication with GitLab added. Resolves issue#10

Type of change

Please delete options that are not relevant to this PR.

• [ ] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also list any relevant details for your test configuration.

• [ ] Automated testing (Feature tests, Unit tests)
• [ ] Manual testing (explain the steps)

Checklist:

• [ ] I have performed a self-review of my own code
• [ ] My changes do not introduce any new warnings or errors
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing tests pass locally with my changes
• [ ] I have used translation helpers and provided translations (where appropriate)

Screenshots (if applicable):

Additional context