Add capability to enforce certain fields for feature definition

For project owners or administrators, they may want certain fields of anchor, key or features to be filled by their users(data scientists), like documentation fields for feature, key description field for key etc.

Project owners or admins should be able to set this in the project yaml config like the following:
```
required fields:
features:
feature_type
feature_documentation
keys:
- key description
```

Relevant code can be found at build_feature(https://github.com/linkedin/feathr/blob/main/feathr_project/feathr/client.py#L214) or tthe logic can be enforced during corresponding object creation phase(https://github.com/linkedin/feathr/blob/main/feathr_project/feathr/feature.py).