This patch fixes 2 issues within strong consistency state machine:
- it might happen that apply is called before the schema is delivered to the node
- on the other hand, the apply may be called after the schema was changed and purged from the schema registry
The first problem is fixed by doing `group0.read_barrier()` before applying the mutations.
The second one is solved by upgrading the mutations using column mappings in case the version of the mutations' schema is older.
Fixes SCYLLADB-428
Strong consistency is in experimental phase, no need to backport.
Closesscylladb/scylladb#28546
* https://github.com/scylladb/scylladb:
test/cluster/test_strong_consistency: add reproducer for old schema during apply
test/cluster/test_strong_consistency: add reproducer for missing schema during apply
test/cluster/test_strong_consistency: extract common function
raft_group_registry: allow to drop append entries requests for specific raft group
strong_consistency/state_machine: find and hold schemas of applying mutations
strong_consistency/state_machine: pull necessary dependencies
db/schema_tables: add `get_column_mapping_if_exists()`
4c8dba15f1