be able to set parameters as required in the client.tsp file

### Clear and concise description of the problem

Hi! I need to be able to mark a parameter as required, but just for one language.

Usually you do that by adding a question mark where the parameter is declared in the routes.tsp file, but I want to be able to do it in the client.tsp file as a customization only for the language I'm working in.

### 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.