The enable_features_on_startup method is adjusted for the raft-based
cluster features. In topology coordinator mode:
- Information about enabled features is taken from system.topology
instead of the usual system.scylla_local (`enabled_features` key).
- Features which, according to the local state, are supported by all
nodes but not enabled yet are also checked. Support for such features
cannot be revoked safely because the topology coordinator might have
performed a successful global barrier and might have proceeded with
marking the feature as enabled.
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