Include supported temporal server version 1.28.0 for poller autoscaling

[krupeshf]

Temporal Affiliation

• I am a Temporal employee

Page URL

https://docs.temporal.io/develop/worker-performance#poller-options

Content Issue

Currently PollerBehaviorAutoscaling is enabled only after temporal server version 1.28.0
Please update the doc to include that.
May be create a Tip/Caution section.

@Quinn-With-Two-Ns explained in a slack thread here