[JIRAALIGN-1780] Feature Backlog: ranking is not saved when moving a feature from unassigned backlog

Issue Summary

On the Feature Backlog page, the user can move items from the Unassigned Backlog into the Backlog and position the Feature in the middle of the existing PI backlog items. However, this ranking assigned by the user is not saved and when the Backlog is refreshed the newly assigned item is at the bottom of the Backlog.

Steps to Reproduce

1. Set your T1 filter to Program and PI
2. Navigate to Backlog > Feature Backlog
3. Make sure you have features in you PI backlog
   
4. Click Unassigned Backlog on the upper right section
5. Move a feature from Unassigned to you PI backlog and put it somewhere in the middle.
   
6. Refresh the page.

Expected Results

The feature added in the PI backlog should retain the position to where it's placed.

Actual Results

If there is no previous ranking recorded on a feature, it will move down to the bottom of the PI backlog.

Workaround

To retain the rank, try to reposition any feature in the PI backlog and just move it back to its previous place. This will manually trigger ranking and retain it.