fix: Set default value for form fields

[ahmadSaeedGoda]

• Use provided default value in struct tags when binding a request input to struct for validation.

Fixes: How to apply default value if empty value provided by client during model binding? #4042, #13042df, #a41721a

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[ahmadSaeedGoda]

@thinkerou @appleboy Kindly review this tiny portion, highly appreciated! 🆒

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.85%. Comparing base (3dc1cd6) to head (497351c).
Report is 69 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4047      +/-   ##
==========================================
- Coverage   99.21%   98.85%   -0.36%     
==========================================
  Files          42       44       +2     
  Lines        3182     2801     -381     
==========================================
- Hits         3157     2769     -388     
- Misses         17       19       +2     
- Partials        8       13       +5     

Flag	Coverage Δ
	?
-tags "sonic avx"	98.84% <100.00%> (?)
-tags go_json	98.84% <100.00%> (?)
-tags nomsgpack	98.83% <100.00%> (?)
go-1.18	?
go-1.19	?
go-1.20	?
go-1.21	98.85% <100.00%> (-0.36%)	⬇️
go-1.22	98.85% <100.00%> (?)
macos-latest	98.85% <100.00%> (-0.36%)	⬇️
ubuntu-latest	98.85% <100.00%> (-0.36%)	⬇️

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