Merge PR #40511 into master

Merge PR #40511 into master

* refs/pull/40511/head:
	qa: update mds_pre_upgrade to no longer stop standbys
	qa: update mds_pre_upgrade to disable standby-replay
	qa: add tests for compat manipulation and upgrade
	doc: remove deprecated compat commands
	doc: update MDS upgrade procedure
	mon,mds: use per-MDS compat to inform replacement
	mon: do not update inline incompat except via mds
	mds: add MDSMap method for creating null MDSMap
	mds: only update beacon epoch if newer
	mds: harden standby_mds lookup
	mon/FSCommands: accept generic ostream rather than stringstream
	include: add less verbose CompatSet dump
	include: add dump operator for Feature
	include: add const qualifier to appropriate CompatSet methods

Reviewed-by: Jos Collin <jcollin@redhat.com>
Reviewed-by: Ramana Raja <rraja@redhat.com>