[4.x] Verify RHOSP branding compliance across docs

[maxwelldb]

Which section(s) is the issue in?

All over the docs, including the Welcome page.

What needs fixing?

Where possible*, replace occurrences of "OpenStack" with {rh-openstack-first} or {rh-openstack}.

• Excludes linked external pages, scripts, CLI output, etc. where replacements could result in confusion or breakage.