Allow registering extension CDN

[philippjfr]

Allows extensions to register a CDN alias for its dist directory, which Panel will use to resolve a resource if in CDN mode. Important for extension paths that are otherwise only available via the custom component path handler (and therefore won't be correctly resolved in static exports, docs and pyodide).

[codecov]

Codecov Report

❌ Patch coverage is 92.85714% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.39%. Comparing base (174aac0) to head (89b5480).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
panel/io/resources.py	94.44%	3 Missing ⚠️
panel/tests/conftest.py	77.77%	2 Missing ⚠️
panel/io/pyodide.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8175      +/-   ##
==========================================
+ Coverage   87.38%   87.39%   +0.01%     
==========================================
  Files         348      348              
  Lines       53779    53836      +57     
==========================================
+ Hits        46994    47050      +56     
- Misses       6785     6786       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.