Send forum posts as md

Closes #1722 (closed)

What does this MR do?

Forum posts are now send as Markdown to the client, where it gets rendered using the frontend md engine, instead of rendering md in the backend, and sending the posts as html. This has multiple advantages:

• Since the markdown engines handle some edge cases differently (examples below), this reduces inconsistencies between the md preview and the actual result
• md is smaller, reduces trafic
• allows to work with the md code in the front end. For example, this makes the option to copy forum post source code trivial. This feature is therefor implemented in this MR as well.

Apart from that, this MR also adjusts the front end md engine to allow escaping chars like \*, which previously only the backend md engine did.

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

confident

Screenshots (if applicable)

Previous inconsistencies:

Test
---
Test

yielded

in preview but

in the forum.

Copying source code

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 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/?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.