[#79445154] Build dashboard urls without any query parameters attached

- `app/extensions/controllers/dashboard.js` checks for the presence of a url and any additional parameters, then strips parameters before building the module slug.
- This is much the same as with the client modifications in #816 (https://github.com/alphagov/spotlight/pull/816/files )
- I've added a test that should show that slugs attached to models should be free of param strings