Future-proof pulse control notebook

**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**