Add explicit includes that were previously available transitively through
service/storage_proxy.hh -> service/storage_service.hh.
This prepares for removing the unused storage_service.hh include from
storage_proxy.hh in a follow-up commit.
Speedup: prerequisite for storage_proxy.hh include chain reduction
(measured -5.8% wall-clock combined with all changes in this series,
same-session A/B: 16m14s -> 15m17s at -j16).
43e337a663