Use Helm storage in manifests

[pkosiec]

Description

1. Modify Helm runner (dependency: Implement Helm release storage backend #677 - agree on Helm Release artifact shape)
   -Remove output.goTemplate. As discussed with @mszostok, we'll keep it to have it as a support for further workflow steps
   - Stop supporting usage of funcs from _helpers.tpl As discussed with @mszostok, we'll keep it to have it as a support for further workflow steps
   • Update JSON Schema for Type
   • Require Helm storage (agree on a given manifest path)
   • Add another output from Helm Runner - create artifact, which puts context for Helm release backend
2. Create a new PostgreSQL and Mattermost Implementation revisions to showcase that the Helm storage works properly.
   • Create Helm Template artifacts on PostgreSQL install and Mattermost install level (put context for Helm storage backend)
   • Create new helm.install Impl revision
   • Create new helm.upgrade Impl revision
   • Out of scope: other manifests than the ones needed for Mattermost installation

Related issues

See epic #650