docs: router HTTP response status codes

[shorgi]

Document router response status codes in new errors page

Resolves #4740 and https://apollographql.atlassian.net/browse/DOC-34

[router-perf]

CI performance tests

• reload - Reload test over a long period of time at a constant rate of users
• events_big_cap_high_rate_callback - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity using callback mode
• events_without_dedup_callback - Stress test for events with a lot of users and deduplication DISABLED using callback mode
• large-request - Stress test with a 1 MB request payload
• const - Basic stress test that runs with a constant number of users
• no-graphos - Basic stress test, no GraphOS.
• step-jemalloc-tuning - Clone of the basic stress test for jemalloc tuning
• events - Stress test for events with a lot of users and deduplication ENABLED
• events_callback - Stress test for events with a lot of users and deduplication ENABLED in callback mode
• events_big_cap_high_rate - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity
• events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• xxlarge-request - Stress test with 100 MB request payload
• xlarge-request - Stress test with 10 MB request payload
• step - Basic stress test that steps up the number of users over time

[abernix]

Also, worth noting that CircleCI is currently in a brown-out for all of today as one of our base images which we still use is being deprecated in Q4. That's not on you — we're on it — but just FYI.

[Meschreiber]

Some wording suggestions on my end, but otherwise LGTM! (Assuming the router team's accuracy review ofc 🙇‍♀️.)