Implement SAML endpoints for APIv4 (#5671)

* Implement SAML endpoints for APIv4

* Fix unit test

* Only disable encryption when removing puplic/private certs

api4/saml_test.go

@@ -0,0 +1,19 @@
+// Copyright (c) 2017 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package api4
+
+import (
+	"testing"
+)
+
+func TestGetSamlMetadata(t *testing.T) {
+	th := Setup().InitBasic().InitSystemAdmin()
+	defer TearDown()
+	Client := th.Client
+
+	_, resp := Client.GetSamlMetadata()
+	CheckNotImplementedStatus(t, resp)
+
+	// Rest is tested by enterprise tests
+}