[BUG] "Set alert status" API doc mentions "in-progress" status instead of "acknowledged"

[peluja1012]

The "set alert status" API docs are outdated. They mention in-progress status, but this status was renamed to acknowledged in 7.15 by this PR. @dplumlee to confirm this update is safe to make.

Doc URL link or topic name:
https://www.elastic.co/guide/en/security/8.5/signals-api-overview.html#_set_alert_status

[dplumlee]

I would say this is a safe update to make. We still support in-progress for backwards compatibility reasons but we should be telling users to use acknowledged as it lines up with the rest of the UI terminology past 7.15