[Feature]: Add subscribe to Node class

[Chrylo]

Description

Only a DataPoint (subclass of a node) has a subscribe method. This forces the developer to force cast from Node to DataPoint when using the following API:

node: DataPoint = self.Vehicle.getNode(signal_str) # type: ignore

_Originally posted by @Chrylo in https://github.com/eclipse-velocitas/vehicle-app-python-sdk/pull/126#discussion_r1615745383_

Suggested Solution

• Implement the subscribe method also for the Node class
• If a node (which is not a DataPoint / Signal) is being subscribed too then subscribe to all children

Alternatives

No response

Additional Context

No response