Expose aggregations for blob search calls to the controller

This is step 2 of the Add search filtering by programming language epic (full plan is detailed in the epic).

Aggregations need to be passed up from the Elasticsearch call to the controller. This should be done at the same time as searches are performed so we don't need to make the search call more than once. There may be some code refactoring required to complete this work (based on what I've seen in the code).

The Elasticsearch aggregation will be added in the search_blob method located in ee/lib/elastic/latest/git_class_proxy.rb