Improve Colab authentication

[giswqs]

This PR improves the Earth Engine authentication and initialization on Colab. If no Colab secrets are detected, use auth_mode="notebook". If the EE_PROJECT_ID serect is deteced, use auth_mode="colab" and ee.Initialize(project=EE_PROJECT_ID).

#1870 (comment)

[github-actions]

🚀 Deployed on https://65a14696c3590f1a50c2def7--opengeos.netlify.app

[giswqs]

It works as expected. Setting EE_PROJECT_ID as a Colab secret. It will use ee.Authenticate(auth_mode="colab") and ee.Initialize() without having to specify a project ID.

[jdbcode]

This is a nice convenience feature! Between this and the reduced clicking of the auth_mode="colab" auth UI it gets people going pretty fast.

I really like your solution for saving the entire credentials though, personally, especially after adding a project to the credentials with earthengine set_project 'YOUR-EE-PROJECT'