Adds a tutorial for single/two qubit heatmaps

[tanujkhattar]

• Adds a tutorial for single / two qubit heatmaps

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[balopat]

A lot of this tutorial Google focused. I'd split it up into two parts:

1. Introduce a new page under Guide - Visualizations - this could have
   a.) Heatmaps
   b.) Circuit diagrams (ASCII, SVG, etc.)
   c.) later will have the bloch sphere, kak and others
2. "Visualizing calibration metrics" would live under docs/tutorials/google

This PR could start with just point 2.)
Also:

• Make sure to have an entry in docs/_book.yaml for it.
• add the authentication setup to one of the cells - otherwise this is not going to run using Quantum Engine on Colab (you can just copy-paste it from docs/tutorials/colab.ipynb)

[balopat]

Thank you!!! LGTM after the final nits

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