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