Insert the GGI summer school "ZNE exercice" notebook into the Examples section of the docs

[andreamari]

Issue Description

On July 2022, we gave some lectures on error mitigation and Mitiq at the GGI Summer School - SQMS. We made an "exercise notebook" for learning how to apply ZNE to a GHZ state with Mitiq.

In the last Mitiq community call, @nathanshammah suggested to port this notebook into the Mitiq docs, in the Examples section.

Proposed Solution

To address this issue, the exercise notebook should be transformed into a myst file, perhaps modified, and finally included in the docs.