Provide a way to check and cancel scheduled email blasts.

[Schwarzschild]

https://docs.sendgrid.com/api-reference/cancel-scheduled-sends/cancel-or-pause-a-scheduled-send

also fix time displayed in admin log to be local time for scheduled messages.

[Schwarzschild]

This sort of works:

% curl --header "Authorization: Bearer $SENDGRID_APIKEY" --header 'Content-Type: application/json' --request POST --url https://api.sendgrid.com/v3/mail/batch          
{"batch_id":"YTljYmQyYzAtYWFkNi0xMWVjLWE2NDQtZWE4MmU5YzNkMWRmLTRhMzdjN2ZkOQ"}

% curl --header "Authorization: Bearer $SENDGRID_APIKEY" --header 'Content-Type: application/json' --request GET --url https://api.sendgrid.com/v3/user/scheduled_sends/ZDZiNGVlNmUtYWFjZS0xMWVjLWE2MGItZmE2YWU4NDBmODU0LTA3MmMyYTUxMg
[]%         ```

[Schwarzschild]

done