Allow to undo the keep as placeholder status and revert to pending_reassignment

Problem

Currently, when an owner marks a placeholder as keep as placeholder, there is no UI option to revert it. If a user makes a mistake and needs to change the status back to pending reassignment, this requires manual intervention via Rails console to update the status, which is costly.

Proposed Solution

Allow owners to undo the keep as placeholder decision

1. Allow users to revert from keep as placeholder status back to pending reassignment via the UI

Benefits

• Improves user experience by allowing self-service correction of mistakes
• Reduces support ticket volume

Acceptance Criteria

• User can change status from keep as placeholder back to pending reassignment via the UI
• Documentation is updated to reflect the new functionality
• Add event tracking for this new action

Technical Notes

• Need to modify the state machine to allow transition from keep_as_placeholder to pending_reassignment