Insight aggregations: Connect aggregation UI with aggregation GQL resolvers (FE/BE integration)

Created by: vovakulikov

Blocked by https://github.com/sourcegraph/sourcegraph/issues/39954 Blocked by https://github.com/sourcegraph/sourcegraph/issues/39776

After we created UI in https://github.com/sourcegraph/sourcegraph/issues/39954 we should connect this UI with aggregation data from the backend. Tech note: for this chart, we should use a regular fetch GQL request and not the compute search stream, as it was originally planned.

/cc @joelkw @felixfbecker @vovakulikov @unclejustin