Prevent stalls in this path as seen in performance testing.
Also, add a respective rest_api test.
Fixes#11114Closes#11115
* github.com:scylladb/scylla:
storage_service: reserve space in get_range_to_address_map and friends
storage_service: coroutinize get_range_to_address_map and friends
storage_service: pass replication map to get_range_to_address_map and friends
storage_service: get_range_to_address_map: move selection of arbitrary ks to api layer
test: rest_api: test range_to_endpoint_map and describe_ring