Helix Operation does not allow UNKNOWN to EVACUATE Operation

[ngngwr]

Describe the bug

Helix does not allow transition of a participant from UNKNOWN to EVACUATE, this blocks Unplanned SWAPs for the cluster

To Reproduce

Create a node with UNKNOWN SWAP Operation,
Try to set the node Operation to EVACUATE

Expected behavior

A clear and concise description of what you expected to happen.
Helix should allow since the node is not yet enabled so the transition should be allowed

Additional context

Add any other context about the problem here.

[xyuanlu]

why we want to set evacuate from unknown? Unknown host don't serve any traffic, so no need to evacuated. Whatever upstream user should check instance state and then determine what next state to be.