insights: use graphql for live preview of search based insights

Created by: chwarwick

As of #34925 graphql has a new searchInsightPreview that supports both capture group and search based insights with 1 or more series.

Migrating to the new preview will allow the webapp to share preview behavior between capture group and search insight types (currently limited to when the insight is restricted to a named set of repositories) and allow the removal of the webapp code that previously generated the preview.