Data contract emitter

### Clear and concise description of the problem

- Typepsec should be centralised specification from where datacontract.yaml / datacontract.json should be generated https://datacontract.com/
- Since Typespec model has all information like schema , data quality rules it can help us in integrate with various other provider.

### Checklist

- [X] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md)
- [X] Read the [docs](https://typespec.io/docs/).
- [X] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.