Add ceph_nfs_adopt tag to the cephadm-adopt playbook

Add ceph_nfs_adopt tag to the cephadm-adopt playbook

There are existing OpenStack scenarios where nfs is still not managed
by cephadm. For this reason sometimes is useful skip the nfs part of
the adoption playbook and leave this daemon unmanaged.
The purpose of this patch is providing a tag to enable the OpenStack
operators to skip this playbook section.

Closes: https://bugzilla.redhat.com/2009212
Signed-off-by: Francesco Pantano <fpantano@redhat.com>