Make it possible to restore schema into a different DC setting

[Michal-Leszczynski]

As described in #4041 and #3525, starting from SM 3.3 and Scylla 6.0, SM restores schema by applying the output of DESC SCHEMA WITH INTERNALS. As DCs are a part of keyspace schema, it makes it impossible to restore schema into a cluster with different DCs - even though we are aiming to make restore work with any cluster topology.

So right now this is a documented limitation, but we should make it possible to restore schema into a different DC setting or make it easier for the user to modify just the DC part of keyspace schema.

cc: @karol-kokoszka @tzach @mikliapko

[karol-kokoszka]

See #4052 (comment)