This will allow to trigger the read barrier directly via the API,
instead of doing work-arounds (like dropping a non-existent table).
The intended use-case is in the Scylla Manager, to make sure that
the database schema is up to date after the data has been backed up
and before attempting to backup the database schema.
The database schema in particular is being backed up just on a single
node, which might not yet have the schema at least as new as the data
(data can be migrated to a newer schema, but not a vice-versa).
The read barrier issued on the node should ensure that the node should
have the schema at least as new as the data or newer.
Closes#19213
This uses the `trigger_snapshot()` API added in previous commit on a
server running for the given Raft group.
It can be used for example in tests or in the context of disaster
recovery (ref scylladb/scylladb#16683).
