Support the counters feature in tablets keyspaces.
The main change is to fix the counter update during tablets intranode migration.
Counter cell is c = map<host_id, value>. A counter update is applied by doing read-modify-write on a leader replica to retrieve the current host's counter value and transform the mutation to contain the updated value for the host, then apply the mutation and replicate it to other hosts. the read-modify-write is protected against concurrent updates by locking the counter cell.
When the counter is migrated between two shards, it's not enough to lock the counter on the read shard, because in the stage write_both_read_new the read shard is switched, and then we can have concurrent updates reach either the old or the new shard. In order to keep the counter update exclusive we lock both shards when in the stage write_both_read_new.
Also, when applying the transformed mutation we need to respect write_both stages and apply the mutation on both shards. We change it to use `apply_on_shards` similarly to other methods in storage proxy.
The change applies to both tablets and vnodes, they use the same implementation, but for vnodes the behavior should remain equivalent up to some small reordering of the code since it doesn't have intranode migration and reduces to single read shard = write shard.
Fixes https://github.com/scylladb/scylladb/issues/18180
no backport - new feature
Closesscylladb/scylladb#26636
* github.com:scylladb/scylladb:
docs: counters now work with tablets
pgo: enable counters with tablets
test: enable counters tests with tablets
test: add counters with tablets test
cql3: remove warning when creating keyspace with tablets
cql3: allow counters with tablets
storage_proxy: lock all read shards for counter update
storage_proxy: apply counter mutation on all write shards
storage_proxy: move counter update coordination to storage proxy
storage_proxy: refactor mutate_counter_on_leader
replica/db: add counter update guard
replica/db: split counter update helper functions
95700c5f7f