WIP feat(redis): redis client and caching logic

[Avantol13]

⚠️ Work in progress ⚠️

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The style in this PR agrees with black. ✔️

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[paulineribeyre]

in fence i do: check redis; if not in redis: call indexd so i think we could skip checking redis again here. 3 cases:

• request to indexd from another service: we can assume the other service already checked the cache
• request from a user: now that the request reached indexd, it's too late to improve performance
  • the record is in redis: getting from redis instead of the DB doesn't improve performance (i think)
  • it's not in redis: performance is decreased since indexd checks both