Add new columns to the `system.topology` table: `shard_count` and
`ignore_msb`. When a node bootstraps or restarts and observes that the
values stored in `topology` are different than the local values, it
updates them. This is done in the `update_topology_with_local_metadata`
function (the 'metadata' here being the two values).
Additional flag persisted in `system.scylla_local` is used to safely
avoid performing read barriers when the values didn't change on node
restart. A comment in `update_topology_with_local_metadata` explains why
this flag is needed.
An example use case where `shard_count` and `ignore_msb` are needed is
creating CDC generations.
Fixes: #13508
f9051dccaa