Draft: Resolve "Revise template logic for contentSecurityPolicy"

What does this MR do?

Changes template logic such that CSP settings are always emitted into the gitlab.yml, whether enabled or disabled.

Related issues

Closes #2755 (closed)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
  • Could not find one pre-existing for CSP. If this is needed, some pointers would be appreciated.
• Equivalent MR/issue for omnibus-gitlab opened
  • Previously done via: gitlab-org/omnibus-gitlab!5210 (merged), as part of gitlab-org/gitlab#30720