[7.x] Add support for peer recoveries using snapshots after primary failovers #79137
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This commit adds support for peer recoveries using snapshots after
a primary failover if the snapshot shares the same logical contents
but the physical files are different. It uses the seq no information
stored in the snapshot to compare against the current shard source
node seq nos and decide whether or not it can use the snapshot to
recover the shard. Since the underlying index files are different
to the source index files, error handling is different than when
the files are shared. In this case, if there's an error while
snapshots files are recovered, we have to cancel the on-going
downloads, wait until all in-flight operations complete, remove
the recovered files and start from scratch using a fallback
recovery plan that uses the files from the source node.
Relates #73496
Backport of #77420