The frontend create/delete role buttons on
Identity>Roles page rely on a backend config
OPENSTACK_KEYSTONE_BACKEND that is defined in
the config file. However, the setting is not being
returned to the frontend because there is another
setting called REST_API_REQUIRED_SETTINGS that lists
the settings that are returned to the frontend.
This patch adds OPENSTACK_KEYSTONE_BACKEND to
REST_API_REQUIRED_SETTINGS which was also done upstream
on commit 9c19b07 back in 2019.
Closes-bug: #2056377
Change-Id: Ia8a18e66610f7149399fe1614b1e515ecf799f55
57ffb4384c