DEV: deprecate `invite.via_email` in favor of `invite.emailed_status`
This commit adds a new column `emailed_status` in `invites` table for
tracking email sending status.
0 - not required
1 - pending
2 - bulk pending
3 - sending
4 - sent
For normal email invites, invite record is created with emailed_status
set to 'pending'.
When bulk invites are sent invite record is created with emailed_status
set to 'bulk pending'.
For invites that generates link, invite record is created with
emailed_status set to 'not required'.
When invite email is in queue emailed_status is updated to 'sending'
Once the email is sent via `InviteEmail` job the invite emailed_status
is updated to 'sent'.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
Arpit Jalan
Sam Saffron
Gerhard Schlager
Louis Rose