Add more oauth logging and note about GitLab ToS for login (#8949)

i18n/en.json

@@ -2842,6 +2842,10 @@
     "id": "api.user.complete_switch_with_oauth.blank_email.app_error",
     "translation": "Blank email"
   },
+  {
+    "id": "oauth.gitlab.tos.error",
+    "translation": "GitLab's Terms of Service have updated. Please go to gitlab.com to accept them and then try logging into Mattermost again."
+  },
   {
     "id": "api.user.complete_switch_with_oauth.parse.app_error",
     "translation": "Could not parse auth data out of {{.Service}} user object"