Introduce TLS Settings for go-micro based http services

TLS for the services can be configure by setting the "OCIS_HTTP_TLS_ENABLED",
"OCIS_HTTP_TLS_CERTIFICATE" and "OCIS_HTTP_TLS_KEY" environment variables.
Currently the ocis proxy is this only service that directly accesses backend
services. It determines whether to use TLS or not by looking a the new registry
metadata "use_tls". As specific CA Cert for certificate verification
can be set with the "PROXY_HTTPS_CACERT" environment variable.

services/proxy/pkg/command/server.go

@@ -72,10 +72,13 @@ func Server(cfg *config.Config) *cli.Command {
 
 			m.BuildInfo.WithLabelValues(version.GetString()).Set(1)
 
-			rp := proxy.NewMultiHostReverseProxy(
+			rp, err := proxy.NewMultiHostReverseProxy(
 				proxy.Logger(logger),
 				proxy.Config(cfg),
 			)
+			if err != nil {
+				return fmt.Errorf("Failed to initialize reverse proxy: %w", err)
+			}
 
 			{
 				server, err := proxyHTTP.Server(