feat(fs): Implement loading HTML from http.FileSystem

[sunshineplan]

fixed #2795

This pull request implements the functionality to load HTML templates directly from an http.FileSystem. The changes aim to enhance the framework's flexibility in handling HTML templates by introducing support for http.FileSystem.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.86%. Comparing base (3dc1cd6) to head (eb4a5e1).
Report is 104 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4053      +/-   ##
==========================================
- Coverage   99.21%   98.86%   -0.36%     
==========================================
  Files          42       44       +2     
  Lines        3182     2811     -371     
==========================================
- Hits         3157     2779     -378     
- Misses         17       19       +2     
- Partials        8       13       +5     

Flag	Coverage Δ
	?
-tags "sonic avx"	98.85% <100.00%> (?)
-tags go_json	98.85% <100.00%> (?)
-tags nomsgpack	98.83% <100.00%> (?)
go-1.18	?
go-1.19	?
go-1.20	?
go-1.21	98.85% <100.00%> (-0.37%)	⬇️
go-1.22	98.85% <100.00%> (?)
macos-latest	98.85% <100.00%> (-0.37%)	⬇️
ubuntu-latest	98.85% <100.00%> (-0.37%)	⬇️

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[erik-nilcoast]

This would have just saved me some issues in production :). It'd be great if gin supported this.