Re-enable previously persisted enabled features on node
startup. The features list to be enabled is read from
`system.local#enabled_features`.
In case an unknown feature is encountered, the node
fails to boot with an exception, because that means
the node is doing a prohibited downgrade procedure.
Features should be enabled before commitlog starts replaying
since some features affect storage (for example, when
determining used sstable format).
This patch implements a part of solution proposed by Tomek
in https://github.com/scylladb/scylla/issues/4458.
Tests: unit(dev)
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
1365e2f13e