fix: copy the metadata of the ImageCollection when copying an asset

[12rambau]

Fix #371

It was much more complicated than I though.
Setting the system:time_start of the ImageCollection is forcing me to jump in 3 differnet naming convention:

• startTime in the getAsset method
• start_time in the updateAsset method
• system:time_start (still camel case but reversed) in ee.imageCollection.propertynames

In this PR I upgraded the setProperties so it supports all type of properties (system and normal) and tay consistent with the server API convention (system:time_start).
I then added extra steps in the copy method to retreive startTime from the original asset and pass it in the correct format.

I also reported my findings on the Google issue tracker: https://issuetracker.google.com/issues/381535044

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.21%. Comparing base (39054f7) to head (7eb8000).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #388      +/-   ##
==========================================
- Coverage   89.76%   89.21%   -0.55%     
==========================================
  Files          27       27              
  Lines        1739     1753      +14     
  Branches       87       92       +5     
==========================================
+ Hits         1561     1564       +3     
- Misses        151      160       +9     
- Partials       27       29       +2     

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