httpjson: support configurable response_timeout

[gam-phon]

There is no configurable response_timeout in httpjson input. I have an endpoint that takes more than the default timeout to response.

Here is the default response_timeout, which is hard coded, for httpjson:

        tr := &http.Transport{
            ResponseHeaderTimeout: time.Duration(3 * time.Second),
            TLSClientConfig:       tlsCfg,
        }
        client := &http.Client{
            Transport: tr,
            Timeout:   time.Duration(4 * time.Second),
        }

[gam-phon]

I have opened a pull request to add this.

[sparrc]

closed by #1651