Enhancement: Support Scalar configuration

[FHU-yezi]

Summary

While researching the Scalar project, I found that some custom config is avaliable, the full list can be found here: https://github.com/scalar/scalar/blob/main/documentation/configuration.md.

Basic Example

There are an example from Scalar repo, for FastAPI, and support config: https://github.com/scalar/scalar/blob/main/packages/scalar_fastapi/scalar_fastapi/scalar_fastapi.py.

We need to change this file: https://github.com/litestar-org/litestar/blob/main/litestar/openapi/plugins.py#L351, ScalarRenderPlugin, to support this new feature. I also expect the config will be fully typed with Pydantic.

Drawbacks and Impact

I don't think this enhancement will comes with any drawbacks to current users.

Unresolved questions

Maybe we should also support to pass the config directly to Scalar in case of new config items added and we can use them without a Litestar update.