Update "Compare to Calibration" tutorial into "Identifying Hardware Changes" with Simultaneous Readout and additional context (quantumlib#4552)

A large rework of the "Compare to Calibration" tutorial to emphasize the use of Parallel XEB and Simultaneous Readout (new) to identify if and how qubits have drifted since the previous maintenance calibration. Adds contextual information on what drift is, how it occurs, and what you can do about it once spotted. 

TODO/Things I don't have answers for yet: 
- Relative linking for API reference pages
- Need more links/references on qubit picking/mapping/routing. 
- An email address should be supplied for the quantum engine support team at the end of #Heatmap Observations
- Edit: Renaming the file without losing the previous contributors' commit history. 

More importantly, looking for any corrections, feedback or advice on improving this. Thanks!

Author: augustehirth

dev_tools/notebooks/isolated_notebook_test.py

@@ -43,7 +43,7 @@
     # get_qcs_objects_for_notebook
     'docs/tutorials/google/calibration_api.ipynb',
     'docs/tutorials/google/colab.ipynb',
-    'docs/tutorials/google/compare_to_calibration.ipynb',
+    'docs/tutorials/google/identifying_hardware_changes.ipynb',
     'docs/tutorials/google/echoes.ipynb',
     'docs/tutorials/google/floquet_calibration_example.ipynb',
     'docs/tutorials/google/reservations.ipynb',

docs/_book.yaml

@@ -198,8 +198,8 @@ upper_tabs:
         path: /cirq/tutorials/google/start
       - title: "Visualizing calibration metrics"
         path: /cirq/tutorials/google/visualizing_calibration_metrics
-      - title: "Compare to latest calibration"
-        path: /cirq/tutorials/google/compare_to_calibration
+      - title: "Identifying Hardware Changes"
+        path: /cirq/tutorials/google/identifying_hardware_changes
       - title: "Qubit picking with Loschmidt echoes"
         path: /cirq/tutorials/google/echoes
       - title: "Circuit optimization, gate alignment, & spin echoes"

docs/google/calibration_faq.md

@@ -275,7 +275,7 @@ In order to ensure an apt comparison, it is important to keep the following poin
   - Use parallel readout heatmap to avoid any obviously broken qubits.
   - Use two-qubit error heatmaps to choose various patches of qubits with good two-qubit gate performance.
   - Use a mini-benchmark circuit to sanity check both qubit choice and basic circuit design.
-  - If in doubt, [use parallel XEB to check for issues like drift / TLS](../tutorials/google/compare_to_calibration.ipynb).
+  - If in doubt, [use parallel XEB to check for issues like drift / TLS](../tutorials/google/identifying_hardware_changes.ipynb).
 
 * Start small with a low number of qubits (e.g. 2 qubits, with 5-10 layers of 2 qubit gates), and increase the number of qubits 
   and gate depth.