Fixed unecessary emails and add multiple reminder features

Short description on what are changed/implemented in this pull request

Supporting information

• Jira ticket: BB-6639

Discussions

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Dependencies

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Visual changes

Merge deadline

"None" if there's no rush, "ASAP" if it's critical, or provide a specific date if there is one.

Testing instructions

1. Get the devstack working
2. Change it to the current branch(farhaan/bb-6639-fixing-multiple-reminders)
3. Create a recurrence, add reminder of 2 days before the end date, now in the interval period schedule the list for 2 days.
4. Change crontab to use crontab() so that it runs minutely.
5. docker logs -f listaflow-celeryworker-1
6. You should see different mails being printed on the terminal
7. You can play around with multiple values and multiple end date.

Author notes and concerns

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