Document how to expose SSH without NGINX Ingress

Summary

Currently, the documentation does not provide methods to expose SSH in a situation where the use of nginx-ingress is not an option.

Some use cases

• Not able to use built-in nginx-ingress's tcp-configmap functionality (Kong Ingress, Rancher, Minikube)
• Using a Layer 7 loadbalancer for HTTP(S) (e.g. AWS ALB)

Current state

Currently, we only document how to configure the port via tcp-configmap functionality of nginx-ingress, with the assumption that this is how it will be done.

It is possible to configure the charts to make use of an different IP / LoadBalancer from the NGINX ingress controller(s). This can allow for the use of SSH on different hostname, or in environments that are not allowed/capable of using our "standard" setup.

Future state

Documentation present on how to configure the charts to make use of SSH on an alternate hostname, via a separate LoadBalancer / HostPort / etc.

Example

AWS with ALB for HTTP(S), ELB for SSH (tweaks may be needed)

global:
  hosts:
    ssh: ssh.gitlab.domain.tld
gitlab:
  gitlab-shell:
    service:
      type: LoadBalancer
      annotations:
        service.beta.kubernetes.io/aws-load-balancer-backend-protocol: "tcp"
        service.beta.kubernetes.io/aws-load-balancer-type: "elb"
        service.beta.kubernetes.io/aws-load-balancer-internal: "true"