[DOC] Add steps to configure Ingress resource

[git-hyagi]

We could add a section in the documentation with the instructions to configure the operator to deploy the Ingress resources.
For example:

• what are the pre-requisites
  • we can instruct users about the need to let dns configured according to the settings defined on ingress_host
    https://github.com/kubernetes-sigs/external-dns
  • ingress controller should be available and preferably an ingressclass too
• how to configure Pulp CR to enable external access to Pulp using Ingress (show which fields in Pulp CR should be modified)
  • we can describe with an example how to configure Pulp to use ingress