Communication: Fix link rendering for attachments and show uploaded images in chat

[julian-wls]

Description

This PR fixes an issue that caused lecture attachments such as slides and lecture units to not correctly render as links. Furthermore, it changes the ProvideMarkwon composable to use a custom ImageLoader that is generated by a new class called DefaultImageProvider and is capable of handling authorization. DefaultImageProvider has been introduced to request server images and is also used for the course images now. All images that have been uploaded to the server can be displayed now.
This PR will close #61

Important side note:
Although the links to lecture attachments are displayed correctly now, users still face an authorization error and do not get access to the resource. Fixing this issue is outside the scope of this PR.

Screenshots

[FelberMartin]

Tested the functionality, slides and lecture units are displayed correctly, and clicking them navigates to the repsective part of the app. When clicking on slides I get redirected to the browser but I actually do not have to authenticate there. Maybe this is because I was already logged into the server in chrome?

Showing images in the chat works.

[FelberMartin]

I just noticed that when reloading the chat all messages above the chat are jittering, can you have a look at this? The shown chat is on TS0 in "$mo-1"

[TimOrtel]

I just noticed that when reloading the chat all messages above the chat are jittering, can you have a look at this? The shown chat is on TS0 in "$mo-1"

Have you verified that this problem does not occur on the develop branch? Otherwise, I would create an issue and a separate PR for it.

[FelberMartin]

When checking out the branch the reload jittering with images still persist, but tbh I think we should create a separate issue / PR for this at this point and get this PR merged, I think people are waiting for the fixes and features of this PR

[julian-wls]

When checking out the branch the reload jittering with images still persist, but tbh I think we should create a separate issue / PR for this at this point and get this PR merged, I think people are waiting for the fixes and features of this PR

I agree. I noticed that if the images are smaller than the default height, there is jittering. For images that have a greater original height, it doesn't happen.
You can see this on TS1 in the #random chat of Practical Course: Interactive Learning WS24/25. There is an image in the chat, which acts as an example for the explained behavior.