Reduce memory consumption of Projects::CompareController#show (top-1 count)

This endpoint is the most called (the count column in the report) endpoint during the last 14 days which uses a significant amount of memory (json.mem_bytes>10e9 OR json.mem_objects>10e6).

The report: https://log.gprd.gitlab.net/goto/51df0e2febdcb8d000ceb8f6deb1112c

Details

json.meta.caller_id.keyword: Descending	json.method.keyword: Descending	Count	50th percentile of json.mem_bytes	95th percentile of json.mem_bytes	99th percentile of json.mem_bytes	50th percentile of json.mem_objects	75th percentile of json.mem_objects	95th percentile of json.mem_objects	99th percentile of json.mem_objects
Projects::CompareController#show	GET	4,406	1,094,352,721.815	1,491,490,479.2	1,951,187,703.88	19,539,013.54	21,657,527.728	22,978,915.36	47,643,826.28