In `ks_prop_defs::as_ks_metadata(...)` a default initial tablets count
is set to 0, when tablets are enabled and the replication strategy
is NetworkReplicationStrategy.
This effectively sets _uses_tablets = false in abstract_replication_strategy
for the remaining strategies when no `tablets = {...}` options are specified.
As a consequence, it is possible to create vnode-based keyspaces even
when tablets are enforced with `tablets_mode_for_new_keyspaces`.
The patch sets a default initial tablets count to zero regardless of
the chosen replication strategy. Then each of the replication strategy
validates the options and raises a configuration exception when tablets
are not supported.
All tests are altered in the following way:
+ whenever it was correct, SimpleStrategy was replaced with NetworkTopologyStrategy
+ otherwise, tablets were explicitly disabled with ` AND tablets = {'enabled': false}`
Fixes https://github.com/scylladb/scylladb/issues/25340Closesscylladb/scylladb#25342
