Replace SwiftMailer with Symfony mailer

Closes #1188 (closed), part of #1065 (closed)

What does this MR do?

SwiftMailer is not maintained anymore and not compatible with PHP 8.

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

Quite sure, because sending mails still works in the dev environment.

How to test

1. Checkout branch locally
2. Run ./scripts/composer update symfony/mailer to update the package
3. Login as foodsaver
4. Do something that triggers an email, for example open a forum thread and choose to notify by email
5. See on http://localhost:18084/ the outgoing emails

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
• 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 that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in the Beta Testing forum: https://foodsharing.de/?page=bezirk&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.

Release notes text in German

Closes #1188 (closed)