Accessing node handle config from WakuNodeHandle

[pete-eiger]

Hello friends, for Graphcast SDK we would like to be able to access (read) the local Waku node configurations (a WakuNodeConfig struct) directly from a WakuNodeHandle instance.

For instance, here's how we would instantiate a handle:

let node_handle = waku_new(Some(node_config)).unwrap().start().unwrap();

Later on, we would like to be able to call node_handle.filter or node_handle.config.filter or any other relevant field.

Bonus: if you could add the Display trait to WakuNodeHandle that would help a lot with debugging