[Breaks binary compatibility] Replace `EventualCassandraConfig.ConsistencyConfig` by `CassandraConsistencyConfig`

[rtar]

This new class is reused by upcoming snapshotter, but the old one is kept to keep binary compatibility with the previous versions.

The task should be implemented in a first non-binary compatible version. Also the deprecated EventualCassandraConfig.ConsistencyConfig class itself should be removed.

See #588 for more details.