server/embed/config: Fix configs to support multi CN / multi hostnames

Follow up on the Cherry-pick of [etcd-io#13445](etcd-io#13445)
Allowing the config file of the security config to use multi allowedCN and multi Allowed Hostnames

This won't be cross compatible, if we want to upstream this we need to allow for both AllowedCN and AllowedCNs

server/embed/config.go

@@ -443,15 +443,15 @@ type configJSON struct {
 }
 
 type securityConfig struct {
-	CertFile        string `json:"cert-file"`
-	KeyFile         string `json:"key-file"`
-	ClientCertFile  string `json:"client-cert-file"`
-	ClientKeyFile   string `json:"client-key-file"`
-	CertAuth        bool   `json:"client-cert-auth"`
-	TrustedCAFile   string `json:"trusted-ca-file"`
-	AutoTLS         bool   `json:"auto-tls"`
-	AllowedCN       string `json:"allowed-cn"`
-	AllowedHostname string `json:"allowed-hostname"`
+	CertFile         string   `json:"cert-file"`
+	KeyFile          string   `json:"key-file"`
+	ClientCertFile   string   `json:"client-cert-file"`
+	ClientKeyFile    string   `json:"client-key-file"`
+	CertAuth         bool     `json:"client-cert-auth"`
+	TrustedCAFile    string   `json:"trusted-ca-file"`
+	AutoTLS          bool     `json:"auto-tls"`
+	AllowedCNs       []string `json:"allowed-cns"`
+	AllowedHostnames []string `json:"allowed-hostnames"`
 }
 
 // NewConfig creates a new Config populated with default values.
@@ -631,8 +631,8 @@ func (cfg *configYAML) configFromFile(path string) error {
 		tls.ClientKeyFile = ysc.ClientKeyFile
 		tls.ClientCertAuth = ysc.CertAuth
 		tls.TrustedCAFile = ysc.TrustedCAFile
-		tls.AllowedCN = ysc.AllowedCN
-		tls.AllowedHostname = ysc.AllowedHostname
+		tls.AllowedCNs = ysc.AllowedCNs
+		tls.AllowedHostnames = ysc.AllowedHostnames
 	}
 	copySecurityDetails(&cfg.ClientTLSInfo, &cfg.ClientSecurityJSON)
 	copySecurityDetails(&cfg.PeerTLSInfo, &cfg.PeerSecurityJSON)