Enable pedestrians to walk in heading direction without using a trajectory

Describe the feature

Currently (as of 1.2) it is only possible to make pedestrians walk in a certain direction using a trajectory when using the default controller. This is frustrating for scenario modelers who simply want to let a pedestrian walk in his initial heading direction with an AbsoluteSpeedAction. This is also related to #268 and would make it easier to use a synchronize action with pedestrians.

Describe the solution you would like

I suggest to extend the speed action to be able to specify if the entity should move along the current lane or in its heading direction.

Describe alternatives you have considered

Add a new action that is a "movement direction action" or something like that.

Describe the backwards compatibility

This should be backwards compatible since the default could be follow lane like in the current/old version.

Additional context

Related to #268.