Docs: add documentation about default ingress helm value, corrections to only ingress section (#7943)
Docs: add documentation about default ingress helm value, corrections to only ingress section (#7943)

* add explanation about ingressClassResource.default for helm users

Also cleaned up the entire "I have only one instance of the
Ingress-NGINX controller in my cluster" section

* docs: default ingressclass only when running one controller

* fix link to what is the flag watch ingress

* clarify usage of default ingress class annotation
kubernetes/ingress-nginx,kubernetes/ingress-nginx,kubernetes/ingress-nginx,kubernetes/ingress-nginx,kubernetes/ingress-nginx