Add proxy option for yb-support-tool

[ckamaleo]

For Some customers with security restrictions, its not supported to directly access public Servers from Database Servers.

Any connection attempted from DB nodes are sent to a Proxy/agent in-between (Inside Customer Infra) and then it gets forwarded to Yugabyte Files Server.

Filing this issue requesting to add Proxy Support (As an option when running yb-support-tool)

[ionthegeek]

This seems straightforward - we may be able to enable this with a one-line change to the golang http client configuration:
https://stackoverflow.com/questions/51845690/how-to-program-go-to-use-a-proxy-when-using-a-custom-transport