fix: keep default asset when reloading

[12rambau]

Fix #596

I simply moved the default_asset addition into the _get_items method.
I also trigger the full _get_items when the default_asset is changed

from sepal_ui import sepalwidgets as sw 

widget = sw.AssetSelect(default_asset=["users/bornToBeAlive/random300"])
widget

widget.default_asset = ["users/bornToBeAlive/random150"]

[codecov]

Codecov Report

Merging #607 (2bf9b87) into main (7f1e314) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #607      +/-   ##
==========================================
- Coverage   92.21%   92.20%   -0.02%     
==========================================
  Files          36       36              
  Lines        3892     3886       -6     
==========================================
- Hits         3589     3583       -6     
  Misses        303      303              

Impacted Files	Coverage Δ
sepal_ui/sepalwidgets/inputs.py	100.00% <100.00%> (ø)

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[12rambau]

@dfguerrerom just ignore the codecov patch value, input.py is covered at 100% there is nothing I can add.

[dfguerrerom]

simplier!