Bind: return 413 status code when error is http.MaxBytesError

[ItalyPaleAle]

The Go standard library includes a method http.MaxBytesReader that allows limiting the request body. For example, users can create a middleware like:

func MiddlewareMaxBodySize(c *gin.Context) {
	// Limit request body to 100 bytes
	c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, 100)
	c.Next()
}

When the body exceeds the limit, reading from the request body returns an error of type http.MaxBytesError.

This PR makes sure that when the error is of kind http.MaxBytesError, Gin returns the correct status code 413 (Request Entity Too Large) instead of a generic 400 (Bad Request).

[appleboy]

build fail.

[ItalyPaleAle]

build fail.

@appleboy looks like it's failing on the master branch too: https://github.com/gin-gonic/gin/actions/runs/7814638661/job/21316374466

Reason is that the "go.mod" file now uses Go 1.20, so the CI fails with 1.18

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.99%. Comparing base (3dc1cd6) to head (45a4445).
Report is 107 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3841      +/-   ##
==========================================
- Coverage   99.21%   98.99%   -0.23%     
==========================================
  Files          42       41       -1     
  Lines        3182     3376     +194     
==========================================
+ Hits         3157     3342     +185     
- Misses         17       24       +7     
- Partials        8       10       +2     

Flag	Coverage Δ
	?
-tags nomsgpack	98.99% <100.00%> (?)
go-1.18	?
go-1.19	?
go-1.20	?
go-1.21	?
go-1.23	98.99% <100.00%> (?)
go-1.24	98.99% <100.00%> (?)
macos-latest	98.99% <100.00%> (-0.23%)	⬇️
ubuntu-latest	98.99% <100.00%> (-0.23%)	⬇️

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