Object storage index with redis

To be noted: the entire redis content has to fit in memory: Redis is an in-memory but persistent on disk database, so it represents a different trade off where very high write and read speed is achieved with the limitation of data sets that can't be larger than memory.

Persistence https://redis.io/topics/persistence Modules https://redis.io/modules Business model https://redislabs.com/try-free/ Licensing shift https://www.theregister.com/2019/02/22/redis_labs_changes_license_funding_60m/

Discussion at Redis as a K/V store for billions of objects

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Migrated from T3088 (view on Phabricator)