Send weekly project update email to project author

[Aadesh-Baral]

closes #1377
Implementation:

1. Weekly project update email will be sent to the author of the project on every Monday at 00:00 UTC.
2. Only those projects with at least one activity in a particular week i.e. Mapping, Validating, Invalidating, and setting a task as bad imagery will receive email updates.
3. These email notifications can be turned off by users on the user setting page.
4. Can be turned off for instances using environment variable TM_SEND_PROJECT_EMAIL_UPDATES. So that project update emails are not sent from testing instances.

Design template:

[sonarcloud]

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0.0% Duplication