Refactor route assignment to create route first in environment

When assigning a route to an entity it is possible that later we need to refer to that route again e.g. in a DistanceCondition with "RoutingAlgorithm" enum value set to "assignedRoute".
Therefore it would make sense to first create a "Route" in the environment (derived from mantle_api::IRoute) for later reference instead of assigning the waypoints directly to the entity in the FollowRouteControlStrategy.