Complete auditing columns for `users` table

[michplunkett]

What issue are you seeing?

We need to be able to keep track of who approved, confirmed, and disabled users. Essentially, the following columns need to be added/modified for the users table:

• approved_by
• approved -> approved_at and made into a timestamptz
• confirmed_by
• confirmed -> confirmed_at and made into a timestamptz
• disabled_by
• is_disabled -> disabled_at and made into timestamptz