(Feat) Adding composer package support

Overview

Adds Composer package migration support to congregate with comprehensive handling for different package creation scenarios. Being used in Aylo's Migration

https://gitlab.com/gitlab-com/customer-success/professional-services-group/professional-services-delivery/gitlab-professional-services/Quebec-Inc-SM-to-GitLab.com/SOW-3343/-/issues/3

Files Added/Modified

Following the established pattern from other package type implementations:

1. congregate/migration/gitlab/api/composer.py - ComposerPackagesApi class with GitLab Composer API methods
2. congregate/migration/meta/api_models/composer_package.py - ComposerPackage data model
3. congregate/migration/gitlab/packages.py - Updated PackagesClient with migrate_composer_packages method

Implementation Details

Standard Migration Pattern:

• Uses existing Git tags/branches from pipeline refs for package creation
• Handles version format differences (4.0.0 vs v4.0.0)

Edge Case Handling:

• Packages created from deleted feature branches are migrated using temporary branch approach
• Attempts commit SHA directly first (GitLab API limitation: returns 404 Tag Not Found)
• Falls back to temporary branch creation from commit SHA, then cleanup

Migration Approach:

1. Try original pipeline ref (tag/branch)
2. Create missing version tags when needed
3. Temporary branch creation for deleted branch scenarios

Testing

• Successfully migrated 10/10 packages including edge cases
• Handles both existing and missing Git references
• Automatic cleanup of temporary branches

Tasks

• Implement ComposerPackagesApi with tag/branch creation methods
• Add migrate_composer_packages method with multi-tier approach
• Handle deleted feature branch scenario
• Add temporary branch creation and cleanup
• Test with real migration scenario
• Update docs if needed (workflow, runbooks, README, migration metrics, etc.)

Acceptance Criteria

• Composer packages migrate successfully for standard cases
• Edge cases (deleted branches) handled with fallback approach
• Package version names preserved correctly
• Temporary resources cleaned up properly
• Existing UTs pass locally. If you need help updating any tests, refer to our writing tests documentation