Cache rendered API entities for JIRA MR endpoints

I've noticed this endpoint generates a consistently high load of queries: https://dashboards.gitlab.net/d/api-rails-controller/api-rails-controller?viewPanel=2155933118&orgId=1&var-PROMETHEUS_DS=Global&var-environment=gprd&var-stage=main&var-controller=Grape&var-action=All

From an initial investigation it looks easy to cache, which will also have the benefit of speeding it up too.