Part of splitting creating and editing scheduled messages.
Should be merged with final commit in series. Breaks tests.
Removes `scheduled_message_id` parameter from the create scheduled
message path.
For scheduled stream messages, we already limited the `to`
parameter to be the stream ID, but here we return a JsonableError
in the case of a ValueError when the passed value is not an integer.
For scheduled direct messages, we limit the list for the `to`
parameter to be user IDs. Previously, we accepted emails like
we do when sending messages.
This will help us remove scheduled message and reminder logic
from `/messages` code path.
Removes `deliver_at`/`defer_until` and `tz_guess` parameters. And
adds the `scheduled_delivery_timestamp` instead. Also updates the
scheduled message dicts to return `scheduled_delivery_timestamp`.
Also, revises some text in `/delete-scheduled-message` endpoint
and in the `ScheduledMessage` schema in the API documentation.
Lauryn Menard
Aman Agrawal