Http proxy connection can not reuse between pixiu and upstream

[mark4z]

There are two bugs on HTTP proxy.
[ ] We should reuse http.Client and let user custom it in the config, like MaxIdleConnsPerHost, etc.
[ ] We should close Body so that the connection can be reused.
What happened:
routerfiller.go

	req.Header = r.Header

        // creat http client too many times
	cli := &http3.Client{
		Transport: f.transport,
		Timeout:   hc.Timeout,
	}

	resp, err := cli.Do(req)

manger.go

func (hcm *HttpConnectionManager) buildTargetResponse(c *pch.HttpContext) {
	if c.LocalReply() {
		return
	}

	switch res := c.SourceResp.(type) {
	case *stdHttp.Response:
//It is the caller's responsibility to
	// close Body. The default HTTP client's Transport may not
	// reuse HTTP/1.x "keep-alive" TCP connections if the Body is
	// not read to completion and closed.
		body, err := io.ReadAll(res.Body)
		if err != nil {
			panic(err)
		}
		//Merge header
		remoteHeader := res.Header
		for k := range remoteHeader {
			c.AddHeader(k, remoteHeader.Get(k))
		}

What you expected to happen:

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

[jokercoldly]

Please assign it to me.

[mark4z]

Please assign it to me.

as u wish