chore(docs): Replicate custom histograms CHANGELOG to v1.46.0.

[abernix]

In theory https://github.com/apollographql/router/releases/tag/v1.40.0 was the first version in which this was fixed, but we don't recommend running that version for the reasons that are already noted in the CHANGELOG.md.

Therefore, the first version that we recommend using to utilize custom historgrams is https://github.com/apollographql/router/releases/tag/v1.46.0. This updates the CHANGELOG.md to signal that with a note and a duplication of the original CHANGELOG entry.

Original Issue: #4543
Initial PR: #4572
Stabilizing PR: #4771

[github-actions]

@abernix, please consider creating a changeset entry in /.changesets/. These instructions describe the process and tooling.

[router-perf]

CI performance tests

• 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
• step-with-prometheus - A copy of the step test with the Prometheus metrics exporter enabled
• events_without_dedup_callback - Stress test for events with a lot of users and deduplication DISABLED using callback mode
• events - Stress test for events with a lot of users and deduplication ENABLED
• events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• 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
• xlarge-request - Stress test with 10 MB request payload
• const - Basic stress test that runs with a constant number of users
• 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
• step-jemalloc-tuning - Clone of the basic stress test for jemalloc tuning
• xxlarge-request - Stress test with 100 MB request payload
• demand-control-uninstrumented - A copy of the step test, but with demand control monitoring enabled
• no-graphos - Basic stress test, no GraphOS.
• events_callback - Stress test for events with a lot of users and deduplication ENABLED in callback mode
• large-request - Stress test with a 1 MB request payload
• demand-control-instrumented - A copy of the step test, but with demand control monitoring and metrics enabled