Send emails for new manuscripts

[nuest]

For a fixed lists of users in the database (table with emails) send out an email at a fixed interval (end of the month) with all new manuscripts of that month.

• https://docs.djangoproject.com/en/4.0/topics/email/
• have integration test for email
  • via https://teampkp.slack.com/archives/C5KFSJF6Y/p1649802838683839 with some more insights, and https://github.com/pkp/pkp-docs/blob/main/dev/documentation/en/resources.md#log-emails
  • https://maildev.github.io/maildev/
  • https://github.com/mailhog/MailHog

See also #11 about scheduling - the same scheduling method should be used