Unsupported Openshift content in the codebase

[smlx]

Describe the bug

oc-build-deploy-dind was removed in #3110. However we still have parts of the documentation and codebase which refers to features that only existed in that build system.

Some examples:

• lagoon.yml
  • additional-yaml - Removed in update docs to remove Openshift references #3195, do we need to document/lint that it's deprecated?
  • environments.[name].templates
  • hsts - Support was added back, but the old config should be deprecated
  • monitoring_urls - Deprecate then Remove monitoring_urls #2975

• deprecated flags such as hsts should be removed from the templates.
• deprecated flags should also be removed from the build scripts (this work might be done as part of feat: use build tool to generate ingress templates #3133?)
• all tests which are tagged skip-on-kubernetes should be removed since Lagoon no longer supports any other platform.

To Reproduce

Steps to reproduce the behavior:

1. Go to .lagoon.yml documentation.
2. See unsupported fields in the example, such as monitoring_urls.

Expected behavior

All unsupported content which no longer has effect on Lagoon builds should be removed from across the documentation and codebase.

Screenshots

n/a

Additional context

To help users who have deprecated or unsupported fields in their .lagoon.yml, checks can be added to the deprecated profile in lagoon-linter so that eventually we can put warnings in the build log. Raise issues over there to add the required checks.