create users from existing entities

[ztsai]

• fetch all entities with userId and appId (articles, replyrequests, articlereplyfeedbacks, etc...) and create users for each unique (appId, userId) pair, where the new user id is appId_sha(userId)
• update userId for entities mentioned above
• analytics only has docUserId and no appId, need to refetch all data from replies
• unit tests integration tests

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• design collision handling -> lowered priority and tracked in cofacts/rumors-api#222