Reduce memory consumption of security reports GraphQL calls

While looking at memory use of the GraphQL controller in general, we noticed that something related to processing security reports is consuming a lot of memory and often times out after 1m:

• ~6GB of memory allocated per call
• ~800 external HTTP requests per call

https://log.gprd.gitlab.net/goto/25bdcc4d6b71f27c8d886b8136768b75

Originally reported in &5622 (comment 568733377)