insights: replace default not-supported logic in aggregation resolver to run the aggreations

Created by: chwarwick

The initial schema and resolvers for aggregations were built to return a not-supported response by default.
After https://github.com/sourcegraph/sourcegraph/issues/40207 provides the ability to group the search response and https://github.com/sourcegraph/sourcegraph/issues/40205 limits the number of responses returned. These capabilities need to be integrated into the resolver to return the grouped data instead of the default response.

note: a limited grouping types may initial be supported and this may need to be extended in the future as new grouping types become available.

/cc @joelkw @felixfbecker @vovakulikov @unclejustin