This is responsible for:
1.) Handling all the incoming requests at the
messages endpoint which have defer param set. This is similar to
send_message_backend apart from the fact that instead of really
sending a message it schedules one to be sent later on.
2.) Does some preliminary checks such as validating timestamp for
scheduling a message, prevent scheduling a message in past, ensure
correct format of message to be scheduled.
3.) Extracts time of scheduled delivery from message.
4.) Add tests for the newly introduced function.
5.) timezone: Add get_timezone() to obtain tz object from string.
This helps in obtaining a timezone (tz) object from a timezone
specified as a string. This string needs to be a pytz lib defined
timezone string which we use to specify local timezones of the
users.