Include `root_path` when looking up assets

[bundabrg]

In patched_get_swagger_ui_html the urls only reference self.app.docs_url. This works fine until the app itself is mounted under another app. When this occurs the mounted app gets the base path passed to it via root_path.

IE:

def create_app() -> FastAPI:
    main_app = FastAPI(...)
    
    app = FastAPI(...)
    StandaloneDocs(app)
    app.include_router(myroute1, prefix='myroute1')
    app.include_router(myroute2, prefix='myroute2')
    
    main_app,mount("/myapp1", app)
    return main_app

In the above case, the full docs url is probably /myapp1/docs, but it then will try to read its static assets from /docs.

To fix this, patched_get_swagger_ui_html should prefix the passed urls to get_swager_ui_html with the apps current root_path.

Something like:

            def patched_get_swagger_ui_html(*args, **kwargs):
                return get_swagger_ui_html(
                    *args,
                    **kwargs,
                    swagger_favicon_url=swagger_favicon_url,
                    swagger_css_url=f"{self.app.root_path}{self.app.docs_url}/swagger-ui.css",
                    swagger_js_url=f"{self.app.root_path}{self.app.docs_url}/swagger-ui-bundle.js",
                )