drt: change default behavior of stop timing (avoiding zero wait time)

[sebhoerl]

This is a follow-up on #2730. There, functionality has been added to give more flexibility to manage stop times in DRT.

In particular, we show that, currently, we can have requests that have a wait time < stopDuration and that vehicles always stop exactly for the stopDuration, not longer not shorter.

The other approach, which seems more coherent, is to always require agents to wait at least stopDuration, which may inflate the time that vehicles idle at a stop.

This scenario only appears when a vehicle is already stopping (picking up / dropping off passengers) and a new pickup is dispatched into that stop task. If the stop is already ongoing for 40s and stopDuration = 60s, the new request will only wait 20s. The updated logic would be that the stop duration is inflated to 100s to make the incoming request wait for 60s.

Consequently, it may make sense to rename stopDuration to minimumStopDuration.

This functionality is already included (see #2730), the present issue is only about inquiring what people think of making this the default behaviour and renaming the config option.