Build pyodide wheels and load from CDN

[philippjfr]

Also adds config.npm_cdn to allow CDN to be consistently configured.

[codecov]

Codecov Report

Merging #3858 (69441b0) into master (11d5833) will decrease coverage by 7.76%.
The diff coverage is 88.57%.

❗ Current head 69441b0 differs from pull request most recent head b4c5f13. Consider uploading reports for the commit b4c5f13 to get more accurate results

@@            Coverage Diff             @@
##           master    #3858      +/-   ##
==========================================
- Coverage   82.94%   75.17%   -7.77%     
==========================================
  Files         224      224              
  Lines       32740    32761      +21     
==========================================
- Hits        27155    24627    -2528     
- Misses       5585     8134    +2549     

Flag	Coverage Δ
ui-tests	?
unitexamples-tests	75.17% <88.57%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
panel/io/convert.py	31.10% <50.00%> (+0.30%)	⬆️
panel/config.py	60.59% <80.00%> (+0.15%)	⬆️
panel/io/notifications.py	64.04% <100.00%> (+0.40%)	⬆️
panel/io/resources.py	87.25% <100.00%> (+0.04%)	⬆️
panel/layout/gridstack.py	54.83% <100.00%> (+0.74%)	⬆️
panel/models/deckgl.py	90.32% <100.00%> (+0.32%)	⬆️
panel/models/echarts.py	88.23% <100.00%> (+0.73%)	⬆️
panel/models/json_editor.py	84.37% <100.00%> (+0.50%)	⬆️
panel/models/katex.py	100.00% <100.00%> (ø)
panel/models/perspective.py	100.00% <100.00%> (ø)
... and 29 more

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