Allow for exhaustive customization of the Swagger UI

[jacksonjacobs1]

Hi devs, thank you for maintaining this excellent package.

Is your feature request related to a problem? Please describe.
There is no way to enable Swagger UI deeplinks:
https://flask-restx.readthedocs.io/en/latest/configuration.html

Furthermore most Swagger configurables are not available to flask-restx users:
https://swagger.io/docs/open-source-tools/swagger-ui/usage/configuration/

Describe the solution you'd like
The Swagger documentation above describes a configUrl parameter which allows configuration to be imported. Exposing this parameter in the flask-restx configuration would allow for complete Swagger UI customization.