Replace ERB in charts servicing containers not using Ruby during runtime

Summary

Replace any ERB for those containers within the Helm chart that do not need Ruby at runtime.

• Consideration to be taken regarding parsing markers, so not to collide with Helm (Default is {{ }}, which is what Helm uses)
• Documentation changes / additions need to CNG & charts/gitlab developer documentation

Actionable

• Determine non-overlapping start/end tags for template: {% %}
• Document the use of the start/end tags in developer guidelines for gomplate usage
• Identify all containers of the CNG in this situation
  • Investigation
  • Containers: Workhorse, Shell, ElasticSearch Indexer, Pages
  • Notes: Container Registry has gomplate, but no use of ERB.

Acceptance criteria

• Tag format Decision is documented, and added to developer guidelines.
• MR for each individual chart identified is merged.