This commit adds token_hash and scopes columns to email_tokens table.
token_hash is a replacement for the token column to avoid storing email
tokens in plaintext as it can pose a security risk. The new scope column
ensures that email tokens cannot be used to perform a different action
than the one intended.
To sum up, this commit:
* Adds token_hash and scope to email_tokens
* Reuses code that schedules critical_user_email
* Refactors EmailToken.confirm and EmailToken.atomic_confirm methods
* Periodically cleans old, unconfirmed or expired email tokens
This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction
