[CLD-6577] Mattermost push-proxy service templating revisit

[phoinixgrr]

Summary

Revisiting service templating for the push-proxy chart.

When service.type is set to LoadBalancer, optionally exposing ports HTTP (80) and HTTPS (443).
This is particularly beneficial in situations where service.type is set to LoadBalancer instead of ClusterIP and/or using Ingress

Service Manifest continues to render as expected

> helm template charts/mattermost-push-proxy 
[...]
# Source: mattermost-push-proxy/templates/service.yaml
apiVersion: v1
kind: Service
metadata:
  name: release-name-mattermost-push-proxy
  labels:
    app.kubernetes.io/name: mattermost-push-proxy
    app.kubernetes.io/instance: release-name
    app.kubernetes.io/managed-by: Helm
    helm.sh/chart:  mattermost-push-proxy-0.10.3
spec:
  type: ClusterIP
  ports:
    - name: mattermost-push-proxy
      port: 8066
      targetPort: 8066
      protocol: TCP
  selector:
    app.kubernetes.io/name: mattermost-push-proxy
    app.kubernetes.io/instance: release-name
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/component: server
---
[...]

Ticket Link

https://mattermost.atlassian.net/browse/CLD-6577