Add Vehicle Registration Number fetching

[krejcar25]

In this PR I implemented another API request, that pulls information about each trip. It pulls uses this information to offer the vehicle registration number as an attribute. It might be useful for public transport enthusiasts.

This PR does increase the amount of requests towards Golemio. It might not be a bad idea to include a config option during setup to enable / disable this feature, simply by adding a condition to dep_board_api.py#L52: https://github.com/dvejsada/PID_integration/blob/01d9a187623574b3d770b8929fc3ca9b5d828cca/custom_components/pid_departures/dep_board_api.py#L52