Prod: Enable FF_ENABLE_DOMAIN_REDIRECT and FF_ENABLE_PROJECT_PREFIX_COOKIE_PATH

What does this MR do?

This enables the FF_ENABLE_DOMAIN_REDIRECT and FF_ENABLE_PROJECT_PREFIX_COOKIE_PATH Feature Flags in GitLab Pages in prod environment.

For more information and risk assessment see the Feature Flag rollout issues:

• Feature flag: FF_ENABLE_DOMAIN_REDIRECT (gitlab-org/gitlab-pages#1087 - closed)
• Feature flag: FF_ENABLE_PROJECT_PREFIX_COOKIE_PATH (gitlab-org/gitlab-pages#1091 - closed)

Note that Feature Flags in Pages are configured using Environment Variables and therefore can't be toggled using chatops.

Verified in below environment:

• Staging: gitlab-org/gitlab-pages#601 (comment 1752794428)
• Pre: gitlab-org/gitlab-pages#601 (comment 1761602731)

Author Check-list

Please read the Contributing document and once you do, complete the following:

• Check if all of the following apply:
  • Assign to the correct reviewer per the contributing document
  • Apply the correct metadata per the contributing document
  • Link to related MRs for applying the changes on other environments
  • Link to related Chef changes
  • If necessary link to a Criticality 4 Change Request issue

Reviewer Check-list

• Check if all of the following apply:
  • Reviewed the diff jobs to confirm changes are as expected
  • No changes shown in the diffs not associated with this MR - This may require a rebase or further investigation

Applier Check-list

• Make sure there is no ongoing deployment for the affected envs before merging (see #announcements slack channel)