Future-proof pulse control notebook

[laurencap]

Is your feature request related to a problem? Please describe.
https://github.com/aws/amazon-braket-examples/blob/main/examples/pulse_control/3_Bell_pair_with_pulses_Rigetti.ipynb

This notebook uses hardcoded qubits:

a=10
b=113

This works for the topology of the current Rigetti devices, but it would be great if the notebook would work for any future Rigetti devices, as well.

Describe the solution you'd like
A random pair of connected qubits can be generated from a given device as follows:

import numpy as np

connectivity = device.properties.paradigm.connectivity.connectivityGraph

qubit_a = np.random.choice(list(connectivity.keys()))
neighbors = connectivity[str(qubit)]
qubit_b = neighbors[np.random.randint(len(neighbors))]

Describe alternatives you've considered