insights: Add capture group aggregation

Created by: CristinaBirkel

Closes https://github.com/sourcegraph/sourcegraph/issues/40211

Description

This adds in capture group aggregation. I copied over some functionality primarily from the compute package, but made a couple small modifications. I don't think we want to take an actual dependency on compute for this in any case.

Let me know if you can think of anything else we need to add here for now--I think it's in a pretty good state though to start testing and make sure it integrates with FE, and we can plan to iterate on edge cases?

Test plan

So far, testing locally, I get a lot of timeouts. But here's a query that worked for me:

{
  searchQueryAggregate(query:"query(s.*)$", patternType: regexp) {
    aggregations(mode: CAPTURE_GROUP, limit: 10) {
      __typename
      ... on ExhaustiveSearchAggregationResult {
        groups {
          label
          count
          query
        }
        otherResultCount
        otherGroupCount
      }
      ... on SearchAggregationNotAvailable {
        reason
      }
    }
  }
}

How else should we be testing this? It looks as expected to me, but let me know what you think!