add mux.HandlePath method (v2)

[ti]

in v2, we can not use internal/httprule from outside, so we need add this new method for add custom pattern from out side.

Brief description of what is fixed or changed

with this feature, People can add custom pattern From outsiede

exmaple

mux.HandlePath("GET", "/v1/user/{user_id}/data", ...)

Other comments

in v1 we can use bellow code, but in v2 the httprule in internal, we can not use it from outside

// HandlePath associates "h" to the pair of HTTP method and path pattern.
func HandlePath(method string, path string, h runtime.HandlerFunc) {
	compiler, err := httprule.Parse(path)
	if err != nil {
		log.Fatalf("Parse path to compiler failed: %v", err)
	}
	tp := compiler.Compile()
	pattern := runtime.MustPattern(runtime.NewPattern(tp.Version, tp.OpCodes, tp.Pool, tp.Verb))
	mux.Handle(method, pattern, h)
}
// exmaple
HandlePath("GET", "/v1/user/{user_id}/data", ...)

[codecov-commenter]

Codecov Report

Merging #1449 into v2 will increase coverage by 0.05%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##               v2    #1449      +/-   ##
==========================================
+ Coverage   59.05%   59.11%   +0.05%     
==========================================
  Files          32       32              
  Lines        3903     3913      +10     
==========================================
+ Hits         2305     2313       +8     
- Misses       1344     1345       +1     
- Partials      254      255       +1     

Impacted Files	Coverage Δ
runtime/mux.go	60.68% <80.00%> (+1.80%)	⬆️

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[ti]

@johanbrandhorst
sorry for I lost some data when rebase from v2, I create a new patch with all the codes and docs from the previous merge request

refer : #1440

[johanbrandhorst]

Thank you for your contribution!