* adds proxy_url support,
adds proxy_url to the dockerswarm, eureka, kubernetes and consul service discovery,
adds proxy_url to the scrape_config for targets scrapping,
http based proxy is supported atm,
https://github.com/VictoriaMetrics/VictoriaMetrics/issues/503
* fixes imports
The upstream fasthttp may contain issues like 996610f021 ,
plus a code that isn't used by VictoriaMetrics. So let's use a private copy under our control instead.