cephfs-mirror: add mirror peers via bootstrapping
Right now, adding a peer requires peer cluster ceph configuration and user keyring to be available in the primary cluster (hosts running ceph-mgr and the mirror daemons). This can be avoided by storing the peer monitor host address and user key in mon config store.
Bootstrap the peer by creating a bootstrap token. This token can be imported in the primary cluster and the relevant auth creds will be stored in mon config store.