Revert docs for for now-"yanked" v1.28.0

[BrynCooke]

We have discovered an issue with comment parsing in graphql schema in this release (#3680).

To prevent issues for our users we have decided to yank this release. Users should use 1.27.0 until we fixed the issue and released 1.28.1.

This commit reverts our documentation and also points install.sh back to 1.27.0.

[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.