Create a "setup" script

[Shpigford]

In an effort to make it as easy as possible to get up and running with Maybe, we should have a "setup" script to run.

I'm not attached to any specific method for that (and realistically don't have a lot of experience in this area), so open to suggestions.

The big things that need to happen are around database setup, specifically with rails db:setup and :migrate and then creating a read-only role.

After database setup, a read-only ai_user needs to be created:

CREATE ROLE ai_user WITH LOGIN PASSWORD 'YOUR_UNIQUE_PASSWORD';

GRANT SELECT ON balances TO ai_user;
GRANT SELECT ON accounts TO ai_user;
GRANT SELECT ON connections TO ai_user;
GRANT SELECT ON conversations TO ai_user;
GRANT SELECT ON holdings TO ai_user;
GRANT SELECT ON investment_transactions TO ai_user;
GRANT SELECT ON messages TO ai_user;
GRANT SELECT ON metrics TO ai_user;
GRANT SELECT ON securities TO ai_user;
GRANT SELECT ON security_prices TO ai_user;
GRANT SELECT ON transactions TO ai_user;

And then after that, READONLY_DATABASE_URL needs to be set to postgres://ai_user:YOUR_UNIQUE_PASSWORD@localhost/maybe_ai_development in the .env file.