Merge branch 'djadmin-fix-openapi-relative-instance' into 'master'

Fix openapi viewer for relative url instances

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/114542



Merged-by: Himanshu Kapoor <info@fleon.org>
Approved-by: Tomas Bulva <tbulva@gitlab.com>
Approved-by: Himanshu Kapoor <info@fleon.org>
Co-authored-by: Dheeraj Joshi <djoshi@gitlab.com>