Add jpeg support for JPG pane

[philippjfr]

Supersedes #4427
Fixes #4420

[codecov]

Codecov Report

Merging #4532 (57b957f) into main (4b7d8bf) will decrease coverage by 3.15%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #4532      +/-   ##
==========================================
- Coverage   73.49%   70.34%   -3.15%     
==========================================
  Files         250      250              
  Lines       36519    36526       +7     
==========================================
- Hits        26839    25696    -1143     
- Misses       9680    10830    +1150     

Flag	Coverage Δ
unitexamples-tests	70.34% <100.00%> (-3.15%)	⬇️

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Impacted Files	Coverage Δ
panel/pane/image.py	87.50% <100.00%> (+0.15%)	⬆️
panel/tests/pane/test_image.py	100.00% <100.00%> (ø)

... and 18 files with indirect coverage changes

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