mgr/smb: remove embedded join source and users and groups types

mgr/smb: remove embedded join source and users and groups types

Drop the embedded versions of the join source and usrers and groups
configs from the cluster resource type. This means that potentially
sensitive information is *always* stored in a separate resource
from the less-sensitive general cluster config. Future changes can
then make security related choices about those specific resources
without worrying about having embedded variants inside the cluster.

For convenience I added a new "emtpy" users and groups source type that
can be used for testing. It defines *no* users and groups (an empty set
basically). This wouldn't be useful in a production scenario today as it
would deploy an smbd that you couldn't log into. But for unit testing
it's extremely handy, and maybe it can be used for integration testing
too.

This is a large change because lots of unit tests relied on embedded
join auths or users-and-groups. I tried to handle all the breaking
changes in one go for bisect-ability.

Signed-off-by: John Mulligan <jmulligan@redhat.com>