Resolve "Allow disabling mails for open slots in managed stores"

Closes #1941 (closed)

What does this MR do?

Allows to disable pickup warning mails.

How confident are you it won't break things if deployed?

confident. One problem with beta and prod though: Changing the settings will be possible in beta, while the changes to what mails actually get send only take effect after the next release.

Links

https://beta.foodsharing.de/region?bid=2296&sub=forum&tid=227240&pid=1452632#post1452632

Screenshots (if applicable)

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• set the "API change" label if changes in the API are not backward compatible
• added to the next milestone (see https://gitlab.com/foodsharing-dev/foodsharing/-/milestones, unless it has a "for:Dev" label)
• added an entry to CHANGELOG.md
• added a short text in the release notes to /release-notes/YYYY-MM.md
• Once your MR has been merged, you are responsible to create a testing issue in the Beta Testing forum: https://foodsharing.de/region?bid=734&sub=forum. Please change the MRs label to "state:Beta testing".
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...) how this change can be tested.
  • Be aware, that also non technical people should understand.