docs: fix auth rhai example and link

[parkerholladay]

• In Rhai, it is request[.subgraph].body.extensions, the example was missing the .body
• Fix link to rhai example for forwarding headers

Fixes #issue_number

Checklist

Complete the checklist (and note appropriate exceptions) before a final PR is raised.

• Changes are compatible[^1]
• Documentation[^2] completed

Notes

[^1]. It may be appropriate to bring upcoming changes to the attention of other (impacted) groups. Please endeavour to do this before seeking PR approval. The mechanism for doing this will vary considerably, so use your judgement as to how and when to do this.
[^2]. Configuration is an important part of many changes. Where applicable please try to document configuration examples.
[^3]. Tick whichever testing boxes are applicable. If you are adding Manual Tests:
- please document the manual testing (extensively) in the Exceptions.
- please raise a separate issue to automate the test and label it (or ask for it to be labeled) as manual test

[router-perf]

CI performance tests

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

[shorgi]

The circleci tests don't like the change in the router config to authentication.jwt, adding apollographql/router as reviewers to help resolve

[parkerholladay]

I thought I was testing with the latest router, but that sample I was working with still has 1.26.0. I've updated the commit to just include the rhai example and link fixes.