Adapt the new model structure and standalize uris

[TheMeinerLP]

Proposed changes

This PR improves the backend with many new features and cleanup. It helps us to implement pagination for frontend and also improves generation of dart client

Types of changes

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• Bugfix (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 not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

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• I have read the CONTRIBUTING.md
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

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did and what alternatives you considered, etc...