Refactor: Clean up the starlite namespace

[provinzkraut]

We currently export a great many things from the starlite module, which not only makes it a bit cluttered, but also results in a significant impact on startup time, causing trouble when trying to use Starlite for serverless, or other environments where frequent code reloading is required.

The top level starlite module should only include the basic building blocks, for example:

• the Starlite class
• handler decorators (get, post, etc.)
• Controller
• Router
• Request
• Response
• Provide

Not needed are things like:

• AbstractAsyncClassicPaginator
• OpenAPIMediaType
• AbstractAuthenticationMiddleware
• OpenAPIController
• AsyncTestClient

These are not meant to be exhaustive lists of course, and are mainly provided to give an idea of what should be included.

[provinzkraut]

@starlite-api/maintainers Should we also clean up the submodule namespaces in the same manner?

[Goldziher]

certainly