Merge branch 'docs-improve-guidelines-for-omniauth-auth0-integration' into 'master'

docs: Improve guideline for integrating omniauth provider auth0

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/138473



Merged-by: Bojan Marjanovic <bmarjanovic@gitlab.com>
Approved-by: Jon Glassman <jglassman@gitlab.com>
Approved-by: Jonas Larsen <jlarsen@gitlab.com>
Approved-by: Bojan Marjanovic <bmarjanovic@gitlab.com>
Reviewed-by: Bojan Marjanovic <bmarjanovic@gitlab.com>
Co-authored-by: Gerardo <gerardo@b310.de>