Manage backend accounts in postgres

[malteish]

#907 revealed that redis is only ever used for Session creation in the backend, where Session actually refers to an account. As the prisma model already defines an Account, we decided to remove redis and use the existing prisma Account model instead.

These fields exist in Session, if they are not crossed out they should be migrated to Account:

• account: string; -> id
• signedUserProfile: SignedUserProfile; -> must be read from resolver
• token: string; -> deprecated since jwt
• publicMessageHeadUri?: string; -> not used anywhere
• createdAt: number; -> keeping this for future reference
• socketId?: string; -> deprecated since socket manager
• challenge?: string; deprecated since jwt
• profileExtension: ProfileExtension; -> not used in backend
• spamFilterRules?: unknown; -> spam filter does not exist yet, add field if necessary

[malteish]

migration plan:

1. add createdAt field to Account model, populate with now as default
2. replace all getSession (old) or getAccount (new) calls in backend with checkAccountExists that uses prisma as data source
3. test on testing
4. add manual migration that adds accounts in postgres for all sessions in redis
5. test on staging

[malteish]

In the backend, redis is only used to store the "Session". Todo:

• create a table "account" in postgres that can be queried to know if an ens name has signed up with the backend yet
• populate this table from redis through some scripts
• change getSession to use this new postgres datasource
• remove redis from backend

Moved this info here and closed #1089

[malteish]

Estimate: 9 days (3 remaining)