Add troubleshooting docs for release name

Summary

Adds troubleshooting docs to account for release names other than "gitlab", which can lead to some or all of the following:

• UI unreachable
• CertManager challenges failing
• Ingresses not being assigned an address

Closes #548 (closed)

To be improved upon in #774.

Testing

Values used:

apiVersion: apps.gitlab.com/v1beta1
kind: GitLab
metadata:
  name: issue545
spec:
  chart:
    version: "6.1.3"
    values:
      global:
        hosts:
          domain: mydomain.com
          externalIP: my.static.ip.addr
        ingress:
          # workaround for different release name
          class: gitlab-nginx
      certmanager-issuer:
        email: mnielsen@gitlab.com

What to look for:

• UI is accessible
• Ingresses get assigned addresses
• CertManager Challenges pass
• All pods running and healthy

GKE

helm install operator deploy/chart -n gitlab-system
kubectl apply -f mygitlab.yaml -n gitlab-system

OpenShift

task build_operator_openshift
kubectl apply -f .build/operator-openshift.yaml
kubectl apply -f mygitlab.yaml -n gitlab-system