ALTERing tablets-enabled KEYSPACES (KS) didn't account for materialized
views (MV), and only produced tablets mutations changing tables.
With this patch we're producing tablets mutations for both tables and
MVs, hence when e.g. we change the replication factor (RF) of a KS, both the
tables' RFs and MVs' RFs are updated along with tablets replicas.
The `test_tablet_rf_change` testcase has been extended to also verify
that MVs' tablets replicas are updated when RF changes.
Fixes: #20240
(cherry picked from commit 5ac16e29e6)
Closesscylladb/scylladb#21023
750ff26371