Fixes BF-45993.

`sharded_search_network_interruption.js` was migrated to the e2e suites in SERVER-131029 and kept
the mocked original's empty `$search` query verbatim. The mock never validated query content, but a
real mongot rejects it, and on sanitizer variants that rejection could surface instead of the
interruption the test asserts on.

The test now creates a search index and issues a query mongot accepts. It also distributes chunks
across both shards before creating the index, which `createSearchIndex` requires on a sharded
collection.