Setting durations in timeslots can be problematic

[Narigo]

Steps to reproduce

1. Create a shop with multiple timeslots and different opening hours than their min/max possible values
2. Try choosing a ticket with the minimum or maximum duration available
3. See times in slots that should not have these min or max values

What is the current bug behavior?
There is a conceptual issue for timeslots and availabilities currently: Available timeslots can overlap and if the user sets their duration to the maximum available duration, the slots with less maximum duration could be selected with a longer duration (as much as fits).

What is the expected correct behavior?
The tickets should only work in timeslots that allow these min or max times.

Relevant logs and/or screenshots
(Paste any relevant logs - please use code blocks (```...```) to format console output, logs, and code as it's very hard to read otherwise.)

Possible fixes
I see two possible fixes:

1. Kick the concept of having min/max durations on times and have it in shops or
2. Make the /available route aware of the min and max durations as well. The frontend could then be able to decide, which would work out.
   Fix 2. is more complex and I don't think anymore that the big flexibility would be beneficial for end users as I think it is more confusing.

[Narigo]

The duration should be set on the shop only.