mgr/cephadm: adding oauth2-proxy cephadm service

mgr/cephadm: adding oauth2-proxy cephadm service

adding new oauth2-proxy service. The enable_auth flag enables SSO
authentication via the oauth2-proxy service. The user must ensure the
oauth2-proxy service is deployed before enabling this flag in the
mgmt-gateway service.

FQDN related changes: previously, we were obtaining the FQDN using a
call to the Python socket library run inside the container. While this
generally works, the FQDN returned inside a container can sometimes
differ from the one obtained outside the container. This discrepancy
could cause some issues. To ensure consistency, we now use the FQDN
from the inventory, which provides the correct value as recognized on the host.

Signed-off-by: Redouane Kachach <rkachach@ibm.com>