Add export functionality to team model exercises

Is your feature request related to a problem?

In Team exercises most probably the T2 exercises depend on the T1 exercises. Since everything needs to stay consistent the students need to inform their tutor of any changes they apply to, in this example, the T1 exercises. Because if they don't the tutor will find inconsistencies in the T2 exercises. For Text and programming exercises this is quite simple because they can copy their text, modify it and send it. For modelling exercises this is however not really possible. It appears that copying it with C&P is possible however this is planned to be reverted.

Describe the solution you'd like

I think about an export functionality for modeling exercises like in Apollon. It can then be exported as JSON and imported into the Apollon editor. The students can edit this there and send an image or the JSON to the tutor. Important is to not enable the import functionality since this makes cheating easy.

Describe alternatives you've considered

Alternatively the students could be able to edit their submission afterwards (they, as well as the tutor, should still be able to view the original submission including the assessment) and the tutor will see a second diagram which is displayed as the overridden diagram. This could probably be achieved with the already existing submission system. If submissions after the deadline exist (for given team modeling exercises) it will be displayed as overridden model however the last submission before the deadline will be the one that will be assessed.

Maybe this would even be a better solution since it stays within the system.

Additional context

This is a followup for #1579

ls1intum / Artemis