Library options

Currently we have a way for emitter to define options but no way for a library to do so.

We kept the design of option configuration open for this purpose but didn't have a real use case.
Dpg teams want to be able to define some shared DPG options.

```yaml
emit:
- @azure-tools/cadl-python
options:
@azure-tools/cadl-dpg
common-option: "abc"
@azure-tools/cadl-python:
python-specfic: "def"
@azure-tools/cadl-csharp:
csharp-specfic: "xyz"
```

And then the dpg library can expose those common options via an helper.

Would need to expand the `createLibrary` definition to include non emitter options and a way to retrieve the typed options for your library.

Alternative we could have:
- Don't allow any shared option and require the duplication all the time
- Have a `sharedOptions` field in the config that contains a free form option set(means no validation for typo or missing emitter/library)