Use only the body to build the cache key

[felipeelia]

Description of the Change

Since we've introduced the Request ID header, autosuggest won't cache the authenticated request anymore, as we were using the entire request (including headers) to create the cache key. This PR changes that to use just the query body.

How to test the Change

1. Set external object cache
2. Load a page, see the _search request for autosuggest
3. Reload the page, the authenticated request should have 0ms

Changelog Entry

Fixed - Authenticated requests for autosuggest were not being properly cached while using external object cache.

Credits

Props @felipeelia

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.