Add `ChainMonitor::archive_fully_resolved_monitor_channels`
Archives fully resolved channel monitors by adding them to a backup
location and removing them from the primary storage & the monitor set.
This is useful for pruning fully resolved monitors from the monitor
set and primary storage so they are not reloaded on every new new
block connection.
We also add a new function, `archive_persisted_channel` to the
`Persist` trait that writes the monitor to an archive storage and
removes it from the primary storage.