How to run a specific code at the start of each kernel ?

[12rambau]

Describe the bug

context
In the context of my documentation I need to connect to Google Earth Engine services. When doing so I need to authenticate to the API. I can do that in the test suit using dedicated environment variables. I would like to run these few lines of code when launching every kernel and avoid to write it down inside the notebooks everytime.
If possible can you show me how to run a "startup" script ?

expectation
I would like to run the following code in every kernel:

import ee, pytest_gee, os

if "EARTHENGINE_PROJECT" in os.environ:
    pytest_gee.init_ee_from_token()
elif "EARTHENGINE_SERVICE_ACCOUNT" in os.environ:
    pytest_gee.init_ee_from_service_account()
else:
    raise ValueError("Cannot authenticate with Earth Engine.")

PS: I'm not using MyST-NB in the context of jupyterbooks but a Sphinx documentation

Reproduce the bug

NA

List your environment

it is unrelated to jupyter-book