Link Earth Engine to Cloud Projects

[XavierCLL]

Google established that all Earth Engine usage must be linked to Cloud projects; this is the schedule by Google:

• As of June 2024, all new Earth Engine access requires a Cloud project.
• Starting September 16, 2024, we will be limiting quotas* for accounts without Cloud projects, and most new Earth Engine features will only be available to users of Cloud projects.
• Starting November 13, 2024, all Earth Engine access will require a Cloud project.

We need to make the changes in the plugin (before Nov 13):

1. Creating a transition guide (new and existing users), the process of creating and linking a Cloud Project for newbies would be difficult (example guide: https://courses.spatialthoughts.com/gee-sign-up.html)
2. Register the cloud project ID (e.g. with ee.Initalize(project=project-id)), also see https://github.com/gee-community/qgis-earthengine-plugin/issues/143#issuecomment-2030227202
3. Save and restore the cloud project ID (when e.g. restore a Qgis project)

Some of these issues we have discussed here partially: #142

Google document about this change in detail: https://docs.google.com/document/d/1M2WO_--nF7OErnChsLe4Tyt2NOXaYyFdDSLs-ZP8byE/edit?resourcekey=0-otesbid4q7dn3BLCl-3O5Q

[gena]

1. Yes, we will need to add a note about this in docs/FAQ and announce in the Discussion, e.g. beginning of November. That SpatialThought guide looks like a nice instruction to refer to for Code Editor users and then to have similar behaviour in the plugin.

2. I've started working on this to simulate the Code Editor functionality (sing-in/out user + project selection UI). I will probably connect it to default EE CLI auth file to store project and user.

3. It's better to keep QGIS project save/load and EE select Google Cloud project independent from each other. After the project selection functionality will be added, QGIS EE plugin will pick it up and use during ee.Initialize() call, adding project=... there. Though it will have to be tested for all kinds of error situations like: "QGIS existed, Google Project deleted, QGIS started > EE exception".