[Target] Distributions for target waiting times

Enhance the scenario element Target such that one can define a distribution for the waiting times assigned to each agent. This allows for more elaborate waiting scenarios, e.g. agents queueing up in front of/around a target with individual service (waiting) times.

Problem to solve

Currently, a single target XY can have a waiting time (0 by default), i.e. once an agent has reached the target, it has to wait before it is absorbed / can move to the next target. This waiting time is equal for all agents that approach the same target XY. Similar to the spawnTimeDistributions of a source, we now want to be able to define a distribution (from org.vadere.state.scenario.distribution.impl), draw waiting times from this distribution, and hence assign different values to each agent that approaches target XY. The default distribution should be constant with waiting time 0 (same behavior as before). The values drawn from the distribution must be reproducible.

Further details

Note that this change requires the migration of the scenario files, see e.g. 6958f367.