Currently the service levels cache is unnecessarily updated in every call of `topology_state_load()`. But it is enough to reload it only when a snapshot is loaded. (The cache is also already updated when there is a change to one of `service_levels_v2`, `role_members`, `role_attributes` tables.) Fixes scylladb/scylladb#25114 Fixes scylladb/scylladb#23065 Closes scylladb/scylladb#25116