feat(core): add join mixin for repositories

[akshatdubeysf]

Description

Add join mixin for repositories

Fixes #414

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Intermediate change (work in progress)

Checklist:

• [X] Performed a self-review of my own code
• [X] npm test passes on your machine
• [ ] New tests added or existing tests modified to cover all changes
• [X] Code conforms with the style guide
• [ ] API Documentation in code was updated
• [ ] Any dependent changes have been merged and published in downstream modules

[sonarqubecloud[bot]]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
20 Code Smells

No Coverage information
20.8% Duplication

[sonarqubecloud[bot]]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
41 Code Smells

No Coverage information
19.4% Duplication