Normalize all Storage.xxx_add() methods to return a summary
but origin_visit_add() which requires more work to do so.
Note that this will change the way 'raw_extrinsinc_metadata_add()' report statsd metrics: the 'method_name' tag will now remain 'raw_extrinsic_metadata_add' instead of a forged '<type_name>_metadata_add'.
Also properly annotate output of Storage.xxx_add() methods as Dict[str, int] when applicable.
This is especially needed to be able to help writing consistent proxy storages (like the buffer of the tenacious one) and have them properly handly all _add methods the same. For example, the buffer storage is currently only dealing with "core" object types, and extending id to other object types is not as straighforward as it should be.
Migrated from D5643 (view on Phabricator)