insights: determine if query targets a single repo

Created by: chwarwick

Adds a new function to the insights query builder package that can determine if a query is targeting a single repo. This will initially be used as one piece of criteria to determine if a search query is eligible to run additional queries to provide additional insights such as % change over time or a small preview of an insight.

Currently only supports queries with a 1 step query plan.

resolves #39241 (closed)

Test plan

added unit tests pass