chore: split out router events into its own module

[EverlastingBugstopper]

Breaks down ./apollo-router/src/router.rs into its own module ./apollo-router/src/router/mod.rs with a sub-module ./apollo-router/src/router/events/mod.rs that contains all of the streams that we combine to start a router (entitlement, schema, reload, configuration, shutdown, more streams to be added). This change makes adding new events/modifying existing events a bit easier since it's not in one huge giant file to rule them all.

[router-perf]

CI performance tests

• const - Basic stress test that runs with a constant number of users
• events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• no-graphos - Basic stress test, no GraphOS.
• step - Basic stress test that steps up the number of users over time
• reload - Reload test over a long period of time at a constant rate of users
• xlarge-request - Stress test with 10 MB request payload
• 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
• large-request - Stress test with a 1 MB request payload
• events - Stress test for events with a lot of users and deduplication ENABLED
• xxlarge-request - Stress test with 100 MB request payload

[bnjjj]

Just error in the changelog but otherwise LGTM