docs: restore assets in the documentation

[12rambau]

Fix #353

It's a way bigger PR than expected. The disparition of the Asset object from the documentation made me realise that I made a huge mistake when building the files. having a file with the same name as it's unique class (Asset.py, Asset) is crashing the autopai builder becaue it creates a duplicate at the same level in path.sys. This would be irrelevant if we were not dealing with a extention API but as none of our methods are directly called it creates an implicit circular imports of "Asset".

I thus renamed the Asset file into "ee_asset". For consistency I renamed all the other files to ee_<object in snake case>.py. IT IS NOT CHANGING ANYTHING FROM A USER POV.

Also this forced me to revisit the docstring Sphinx roles that is now fully independant from :py:meth:.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.13%. Comparing base (434cd40) to head (47f0d76).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #355   +/-   ##
=======================================
  Coverage   91.13%   91.13%           
=======================================
  Files          27       27           
  Lines        1646     1646           
  Branches       75       75           
=======================================
  Hits         1500     1500           
  Misses        127      127           
  Partials       19       19           

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