fix(mr ci): use gitlab api to fetch default branch with fallback to main when...

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Description

Added API-based branch resolution with fallback to main

• fix(mr ci): use gitlab api to fetch default branch with fallback to main when using -R flag outside repo

Related Issues

Resolves #7700 (closed)

How has this been tested?

• Added tests for new branch resolution functionality
• Tested locally by building CLI

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap

Closes #7700 (closed) Closes #3455 (closed)