Adds simple API versioning for Designate. Designate API minor releases are
additive to the API major revision and share the same URL path. Subsequent
minor versions are a superset of the previous versions of the same major
revision.
Updates the version discovery document to be compliant with OpenStack
version discovery.
Restructures the API reference to provide more information about the
versioning.
Depends-On: https://review.opendev.org/c/openstack/designate-tempest-plugin/+/848323
Change-Id: I13162711b521472ec8b796ced34d0b7107aaed36
39652d7a51