httpclient: add a configuration parameter to skip TLS certificate validation

In this mode, TLS is susceptible to man-in-the-middle attacks.
This should be used only for testing.

config/config.go

@@ -103,6 +103,7 @@ func init() {
 		HTTPConfig: httpclient.Config{
 			Timeout:        20,
 			CACertificates: nil,
+			SkipTLSVerify:  false,
 		},
 	}