The main goal of this PR is to stop cdc_generation_service from calling
system_keyspace::bootstrap_complete(). The reason why it's there is that
gen. service doesn't want to handle generation before node joined the
ring or after it was decommissioned. The cleanup is done with the help
of storage_service->cdc_generation_service explicit dependency brought
back and this, in turn, suddenly freed the raft and API code from the
need to carry cdc gen. service reference around.
Closes#15047
* github.com:scylladb/scylladb:
cdc: Remove bootstrap state assertion from after_join()
cdc: Rework gen. service check for bootstrap state
api: Don't carry cdc gen. service over
storage_service: Use local cdc gen. service in join_cluster()
storage_service: Remove cdc gen. service from raft_state_monitor_fiber()
raft: Do not carry cdc gen. service over
storage_service: Use local cdc gen. service in topo calls
storage_service: Bring cdc_generation_service dependency back
ebc9056237