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/webdav/pkg/config/http.go

@@ -1,5 +1,7 @@
 package config
 
+import "github.com/owncloud/ocis/v2/ocis-pkg/shared"
+
 // CORS defines the available cors configuration.
 type CORS struct {
 	AllowedOrigins   []string `yaml:"allow_origins" env:"OCIS_CORS_ALLOW_ORIGINS;WEBDAV_CORS_ALLOW_ORIGINS" desc:"A comma-separated list of allowed CORS origins. See following chapter for more details: *Access-Control-Allow-Origin* at https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Allow-Origin"`
@@ -10,8 +12,9 @@ type CORS struct {
 
 // HTTP defines the available http configuration.
 type HTTP struct {
-	Addr      string `yaml:"addr" env:"WEBDAV_HTTP_ADDR" desc:"The bind address of the HTTP service."`
-	Namespace string `yaml:"-"`
-	Root      string `yaml:"root" env:"WEBDAV_HTTP_ROOT" desc:"Subdirectory that serves as the root for this HTTP service."`
-	CORS      CORS   `yaml:"cors"`
+	Addr      string                `yaml:"addr" env:"WEBDAV_HTTP_ADDR" desc:"The bind address of the HTTP service."`
+	Namespace string                `yaml:"-"`
+	Root      string                `yaml:"root" env:"WEBDAV_HTTP_ROOT" desc:"Subdirectory that serves as the root for this HTTP service."`
+	CORS      CORS                  `yaml:"cors"`
+	TLS       shared.HTTPServiceTLS `yaml:"tls"`
 }