Deprecate nginx-ingress-controller

[cnvergence]

Description of the feature you would like to add / User story

As part of the bigger story kubermatic/kubermatic#15229, we have decided to proceed with Envoy Gateway as the default implementation of gateway-api.

This issue concerns deprecating the nginx-ingress-controller, first marking it as deprecated and documenting it in the next KKP release(2.30), then ultimately removing the component

Solution details

• mark nginx-ingress-controller as deprecated
• add documentation about deprecation

[cnvergence]

/milestone KKP 2.30

[cnvergence]

/label sig/networking

[csengerszabo]

/transfer docs