search-blitz: add incremental queries to monitor impact of delta indexing strategy on search times

Created by: ggilmore

This PR adds queries to search blitz to monitor the impact of our new experimental incremental indexing strategy on search times.

See https://github.com/sourcegraph/sourcegraph/issues/29731 for more context on incremental indexing.

Test plan

This change doesn't require testing since it only affects search-blitz - an external monitoring tool.