feat: Event feedback forms

[jnms-me]

Doesn't have to be implemented here, but it should have integration at least.

See https://git.zeus.gent/ZeusWPI/drive/issues/210

[Topvennie]

I'm personally going to wait until feedback forms are used for a couple of events (with positive feedback from the users & bestuur) before adding or integrating it.
Other contributors are of course welcome (and encouraged) to add it if they want it earlier.