Add language aggregations for blob search

This is step 1 of the Add search filtering by programming language epic (full plan is detailed in the epic).

Add an aggregation to the blob (code) scoped search calls. This should be completed using Elasticsearch Composite aggregation and only be run for the searches. Any searches which provide count_only calls (used to display counts on the search tabs, should not include the aggregation to reduce load on Elasticsearch.

Benchmarking was done locally, in staging, and in production: &6853 (comment 698221924)