We change the meaning and name of `replication_state`: previously it was meant
to describe the "state of tokens" of a specific node; now it describes the
topology as a whole - the current step in the 'topology saga'. It was moved
from `ring_slice` into `topology`, renamed into `transition_state`, and the
topology coordinator code was modified to switch on it first instead of node
state - because there may be no single transitioning node, but the topology
itself may be transitioning.
This PR was extracted from #13683, it contains only the part which refactors
the infrastructure to prepare for non-node specific topology transitions.
Closes#13690
* github.com:scylladb/scylladb:
raft topology: rename `update_replica_state` -> `update_topology_state`
raft topology: remove `transition_state::normal`
raft topology: switch on `transition_state` first
raft topology: `handle_ring_transition`: rename `res` to `exec_command_res`
raft topology: parse replaced node in `exec_global_command`
raft topology: extract `cleanup_group0_config_if_needed` from `get_node_to_work_on`
storage_service: extract raft topology coordinator fiber to separate class
raft topology: rename `replication_state` to `transition_state`
raft topology: make `replication_state` a topology-global state
aba5667760