[SimulationEngine][HerdManager] Determine if `simulate_animals` is necessary for `HerdManager` and vice versa

[ew3361zh]

With the refactor of SimulationEngine in #2735, HerdFactory is now initialized with simulate_animals which is derived from the SimulationType enum grouping.

3 things to work on in this issue:

1. If simulate_animals is False, do we need to be initializing a HerdManager at all?
2. If we don't need a HerdManager when simulate_animals is False, does HerdManager need to know the value of simulate_animals or can it be assumed that when it's initialized at any point, simulate_animals is True?
3. There is logic in HerdManager that handles simulate_animals that should be addressed/removed if HerdManager doesn't need simulate_animals.

Please investigate.