Add better support for customizing SwaggerUI

[cguyonnet]

I wanted to define some ResponseInterceptor for SwaggerUI but it looked like these options were never actually set (cf. BuilderExtensions:InitUIOption()).

This PR aims at providing better control over SwaggerUI options by:

• decoupling SwaggerForOcelotUIOptions and SwaggerUIOptions
• adding a parameter to UseSwaggerForOcelotUI() to customize SwaggerUI

[Burgyn]

Hi @cguyonnet,

thanks for your PR. Your implementation is clean and correct. Unfortunately, it is a breaking change. I have to release this as a major change. It will be release in a few minutes as 6.0.0.