Draft: Logically split gigantic gitlab-rails spec file

DISCLAIMER: This MR will possibly get broken to smaller ones.

What does this MR do?

Split off the gigantic gitlab-rails spec to smaller, per-setting files. Towards #4585 (closed). I am splitting off tests that check gitlab.yml contents from the main spec. The main spec will check for other actions that the recipe does.

• Redis related settings
• Object storage related settings
  • Consolidated object storage settings
  • Individual object storage settings
• Pseudonymizer settings
• Cron jobs settings
• Omniauth settings
• Sentry settings
• Pages settings
• GitLab application settings
• Incoming Email settings
• Service Desk Settings
• Repositories storages settings
• Mattermost settings
• Smartcard authentication settings
• FortiAuthenticator settings
• FortiToken Cloud settings
• LDAP settings
• GitLab Shell settings
• Seat link settings
• Sidekiq settings
• Gitaly settings
• Geo settings
• Unleash settings
• Prometheus settings
• Consul settings
• Registry settings

Other changes in this MR (should become individual MRs)

1. Ensure worker keys are rendered in gitlab.yml under cron_jobs only if they have a cron defined.
2. Ensure worker keys are rendered in gitlab.yml under omniauth only if defined.
3. Change default value of omniauth_allow_single_sign_on to nil from saml. In documentation, we ask users to explicitly set it to saml if needed. Us setting this default was an oversight.
4. Change default values for GitLab Pages external_http(s|s_proxyv2) settings to be [] instead of nil.
5. Ensure FortiAuthenticator keys are rendered in gitlab.yml only if enabled
6. Ensure FortiToken Cloud keys are rendered in gitlab.yml only if enabled
7. Ensure LDAP keys are rendered in gitlab.yml only if enabled
8. Ensure Unleash keys are rendered in gitlab.yml only if enabled
9. Ensure Prometheus keys are rendered in gitlab.yml only if enabled
10. Ensure Consul keys are rendered in gitlab.yml only if enabled
11. Ensure Registry keys are rendered in gitlab.yml only if enabled

Related issues

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
• Pipeline is green on dev.gitlab.org if the change is touching anything besides documentation or internal cookbooks
• trigger-package has a green pipeline running against latest commit

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
• Equivalent MR/issue for the GitLab Chart opened