Add new console/http loggers (#6066)

- Add console target logging, enabled by default.
- Add http target logging, which supports an endpoint
  with basic authentication (username/password are passed
  in the endpoint url itself)
- HTTP target logging is asynchronous and some logs can be
  dropped if channel buffer (10000) is full

cmd/gateway-main.go

@@ -159,6 +159,9 @@ func StartGateway(ctx *cli.Context, gw Gateway) {
 	// Initialize gateway config.
 	initConfig()
 
+	// Load logger subsystem
+	loadLoggers()
+
 	// Check and load SSL certificates.
 	var err error
 	globalPublicCerts, globalRootCAs, globalTLSCerts, globalIsSSL, err = getSSLConfig()