Improving current json-schema with pydantic

[nguu0123]

• [x] - Data models for common object: Metric, Constraint
• [x] - Data model for QoA4ML report, contract
• [x] - Data model for ROHE contract
• [ ] - Data model for COMPSAC/DT Security Reports
• [x] - Rewrite language and example report to match pydantic model
• [x] - Rewrite QoA4ML class using pydantic models
• [x] Update README

[nguu0123]

Finish the first and second, add new task that we need to rewrite the current language example to match new pydantic model

[nguu0123]

Will look into COMPSAC/DT Security Reports later, closing the issue for now