Persons API should not time out for huge amounts of distinct_ids

[thmsobrmlr]

Due to implementation errors, some customer accumulate a large amount of distinct_ids for a single person (~150k). This leads to the persons api taking longer to load than the load balancer time-out. We should fix the api (again) to load quickly enough.

Customer ticket: https://posthoghelp.zendesk.com/agent/tickets/15011

#18414
#18395