Expose ability to configure GitLab Shells' Service with a specified nodePort when type: NodePort

The following discussion from !629 (closed) should be addressed:

• @dm3ch started a discussion: (+1 comment)

  I have just understood that this change is located in ingress controller subchart.

  But I think such functionality (ability to expose nodePort) would be also useful for installations without ingress controller or external ingress controller.

  So i think https://gitlab.com/gitlab-org/charts/gitlab/blob/master/charts/gitlab/charts/gitlab-shell/templates/service.yaml would be a better place for such thing.

  @WarheadsSE @gdoucet What do you think about this?

Currently, the gitlab/gitlab-shell chart has the ability to set service.type: NodePort, but does not expose service.nodePort as a way to explicitly choose the port vs allowing random allocation.

We should be able to do the following:

spec:
  type: {{ .Values.service.type }}
  ports:
    - port: {{ include "gitlab.shell.port" . | int }}
      targetPort: {{ .Values.service.internalPort }}
      protocol: TCP
      name: ssh
      {{- if (and (eq .Values.service.type "NodePort") (not (empty .Values.service.nodePort))) }}
      nodePort: {{ .Values.service.nodePort | int64 }}
      {{- end }}

cc @dm3ch