feat: add notifications for scheduled application open date

[KrissDrawing]

This PR addresses #6336

• Addresses the issue in full
• Addresses only certain aspects of the issue

Description

Make sure that #6403 and #6397 are reviewed before (as any changes there might change approach here)
it adds cron job for scheduled application open date (which will send an email, same as when publishing without scheduled application open date).
Also adds another variant of email (coming soon) that will be send when scheduledApplicationDate is in future and we publishing listing (so either when we publish automatically, or scheduledPublishAt cron job)

How Can This Be Tested/Reviewed?

Sign for notifications with your email.
have scheduled listing with scheduledApplicationOpenAt in the future.

1. publish it manually
2. Use cron job for publish
3. use cron job for scheduledApplicationOpenAt (LISTING_OPEN_DATE_NOTIFICATION_CRON_STRING this one)

Author Checklist:

• Added QA notes to the issue with applicable URLs
• Reviewed in a desktop view
• Reviewed in a mobile view
• Reviewed considering accessibility
• Added tests covering the changes
• Made corresponding changes to the documentation
• Ran yarn generate:client and/or created a migration when required

Review Process:

• Read and understand the issue
• Ensure the author has added QA notes
• Review the code itself from a style point of view
• Pull the changes down locally and test that the acceptance criteria is met
• Either (1) explicitly ask a clarifying question, (2) request changes, or (3) approve the PR, even if there are very small remaining changes, if you don't need to re-review after the updates