This ensures we have version-specific references to other projects [1].
Note that this doesn't mean the URLs are actually valid - we need to do
more work (linkcheck?) here, but it's an improvement nonetheless.
[1] https://docs.openstack.org/openstackdocstheme/latest/#external-link-helper
Change-Id: Ifb99e727110c4904a85bc4a13366c2cae300b8df
Import all docs from openstack-manuals.
Part of bp: doc-migration
Change-Id: I28bb8ce1f4a8653f176a554d2e95b4423c437972
Co-Authored-By: Stephen Finucane <sfinucan@redhat.com>