mgr: adding CEPH_ARGS to the mgr pod so radosgw-admin can use it

[rkachach]

Ceph dashboard uses radosgw-admin for certain tasks that aren't accessible via the rgw REST API. Due to the absence of a valid ceph.conf file at /etc/ceph/ceph.conf within the mgr pod, radosgw-admin fails to operate, resulting in 500 errors across various 'Object Gateway' views on the dashboard. This change adds CEPH_ARGS environment variable to the mgr pod enabling its propagation and utilization by the dashboard/radosgw-admin for executing rgw commands.

closes: #13255

Testing:

Create a new rook cluster and make sure Dashboard views work correcly: rgw items information is listed without errors. Make sure envs are available on the mgr pod and the radosgw-admin works without issues:

[root@rook-ceph-mgr-a-8449d46459-9ntft ceph]# env | grep -i ceph_args
CEPH_ARGS=-m [v2:10.105.33.195:3300,v1:10.105.33.195:6789] -k /etc/ceph/keyring-store/keyring

[root@rook-ceph-mgr-a-8449d46459-9ntft ceph]# radosgw-admin -n mgr.a realm list
{
    "default_info": "f03de77f-9f7a-4acd-92d9-9615d78ccd11",
    "realms": [
        "my-store"
    ]
}

Which issue is resolved by this Pull Request:
Resolves #

Checklist:

• Commit Message Formatting: Commit titles and messages follow guidelines in the developer guide.
• Reviewed the developer guide on Submitting a Pull Request
• Pending release notes updated with breaking and/or notable changes for the next minor release.
• Documentation has been updated, if necessary.
• Unit tests have been added, if necessary.
• Integration tests have been added, if necessary.