Disable allow_standby_replay during upgrade

During a microceph upgrade (snap refresh), if allow_standby_replay is not disabled on a CephFS filesystem, the active MDS will not failover and the upgrade may stall. The [upstream docs](https://docs.ceph.com/en/reef/cephfs/upgrading/#upgrade-mds-cluster) explain that this should be done prior to upgrade, and that multi-active MDS filesystems should be decreased to one MDS. Microceph does not currently do either of these things to ensure a smooth upgrade. It probably should.

Reproduction steps: https://paste.ubuntu.com/p/pftGj6Pjn9/