More for #9441 with a bit of refactoring.
- IISServerOptions (inproc) are unique from IISOptions (out of proc)
- Move HTTP/2 topic lower in the document (flow felt off by having it before how to enable IISIntegration)
- Remove stop/starting app pool in favor of dropping app_offline (@shirhatti for thoughts)
- Generalize addressing AspNetCore behind IIS (remove reverse proxy stuff).