Implement SAML endpoints for APIv4 (#5671)

* Implement SAML endpoints for APIv4

* Fix unit test

* Only disable encryption when removing puplic/private certs

i18n/en.json

@@ -7,6 +7,10 @@
     "id": "api.post.link_preview_disabled.app_error",
     "translation": "Link previews have been disabled by the system administrator."
   },
+  {
+    "id": "model.client.upload_saml_cert.app_error",
+    "translation": "Error creating SAML certificate multipart form request"
+  },
   {
     "id": "August",
     "translation": "August"