Reduce timeouts on SearchController#count to 5s

What does this MR do?

The current timeout defaults to 15s. Per https://gitlab.com/gitlab-org/gitlab/-/issues/327106 this endpoint consumes a considerable amount of DB time. Since this endpoint is not as essential as the primary task the user is performing (since it is used to generate tab counts for other tabs you aren't searching) it makes sense to reduce the timeout so slower counts don't consume too much resources.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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Related to #327106