insights: improve efficiency snapshots/recordings over some repos

Created by: chwarwick

Currently snapshots/recordings over some repos are running a global query and then filtering out results. This appends a repo filter which is a OR of the named repos in the insight. Same strategy of as the "preview results" of the insight creation UI.

resolves https://github.com/sourcegraph/sourcegraph/issues/36471

Test plan

Unit tests pass Matched new snapshot values for global and scoped insights to search results ensuring they are the same