feat: support tls for etcd client (#1390)

* feat: support tls for etcd client

* chore: fix typo

* refactor: rename TrustedCAFile to CACertFile

* docs: add comments

* fix: missing tls registration

* feat: add InsecureSkipVerify config for testing

core/discov/config.go

@@ -4,10 +4,14 @@ import "errors"
 
 // EtcdConf is the config item with the given key on etcd.
 type EtcdConf struct {
-	Hosts []string
-	Key   string
-	User  string `json:",optional"`
-	Pass  string `json:",optional"`
+	Hosts              []string
+	Key                string
+	User               string `json:",optional"`
+	Pass               string `json:",optional"`
+	CertFile           string `json:",optional"`
+	CertKeyFile        string `json:",optional=CertFile"`
+	CACertFile         string `json:",optional=CertFile"`
+	InsecureSkipVerify bool   `json:",optional"`
 }
 
 // HasAccount returns if account provided.
@@ -15,6 +19,11 @@ func (c EtcdConf) HasAccount() bool {
 	return len(c.User) > 0 && len(c.Pass) > 0
 }
 
+// HasTLS returns if TLS CertFile/CertKeyFile/CACertFile are provided.
+func (c EtcdConf) HasTLS() bool {
+	return len(c.CertFile) > 0 && len(c.CertKeyFile) > 0 && len(c.CACertFile) > 0
+}
+
 // Validate validates c.
 func (c EtcdConf) Validate() error {
 	if len(c.Hosts) == 0 {