Improve Jupyter Preview error handling and error template

[philippjfr]

We now intercept exceptions that occur in the application when running the Jupyter Preview and display the traceback to the user. Additionally I replaced the old, rather gaudy error template with a new cleaner error page:

Fixes #6256

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 71.37%. Comparing base (78d95d4) to head (0bb227d).

Files	Patch %	Lines
panel/io/jupyter_executor.py	0.00%	9 Missing ⚠️
panel/tests/ui/io/test_jupyter_server_extension.py	0.00%	2 Missing ⚠️
panel/io/handlers.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #6496       +/-   ##
===========================================
- Coverage   82.03%   71.37%   -10.66%     
===========================================
  Files         314      314               
  Lines       46351    46358        +7     
===========================================
- Hits        38024    33089     -4935     
- Misses       8327    13269     +4942     

Flag	Coverage Δ
ui-tests	?
unitexamples-tests	71.37% <0.00%> (-0.08%)	⬇️

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