refs https://github.com/TryGhost/Team/issues/1825
- adds 3 new columns to users table for storing email alert preferences for member signups/cancellation
- adds column for new member signup alert
- adds column for paid subscription started alert
- adds column for paid subscription canceled alert
- Updated default fixtures and tests for new columns
refs https://github.com/TryGhost/Team/issues/1822
Exposing the values through the API is restricted behind the alpha flag.
We're exposing the values by default when the flag is enabled for now,
but can reconsider that later.
refs https://github.com/TryGhost/Team/issues/1724
- storing trial period days allows site owners to give free trial for N days to all members signing up on a tier
- by default, all tiers have 0 trial period days(same as no trial)
refs https://github.com/TryGhost/Toolbox/issues/354
- this commit turns the Ghost repo into a monorepo so we can bring our
internal packages back in, which makes life easier when working on
Ghost
