Import can be added automatically or through action

### Clear and concise description of the problem

when user uses something from external library, the corresponding import will be added automatically or through action just like what we have when editing typescript.

### 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.