[AI assisted]: MM-62914: Added MFA authentication for plugin requests as well (#30160)

We wipe the token if MFA authentication is enabled. Also added a test case
to lock in the functionality.

https://mattermost.atlassian.net/browse/MM-62914

```release-note
NONE
```

server/i18n/en.json

@@ -1705,6 +1705,10 @@
     "id": "api.context.404.app_error",
     "translation": "Sorry, we could not find the page."
   },
+  {
+    "id": "api.context.get_session.app_error",
+    "translation": "Session not found."
+  },
   {
     "id": "api.context.get_user.app_error",
     "translation": "Unable to get user from session UserID."