[GF-MIRROR] Session launcher does not list committed images with private label

## Description

Images with a ‘private’ value in the `ai.backend.features` label are filtered out from the image list of WebUI session launcher and can only be used by directly entering their names. If you commit a session created from a private image, the resulting images also inherit the ‘private’ attribute. While these committed images also require direct name entry in the session launcher, the issue is that committed images have a long random UUID appended to their names, making them impossible to input manually.

## How to resolve

Remove the ‘private’ value in the `ai.backend.features` label before committing an image.

We introduced the 'private image' feature to prevent users from viewing other users' private images. The private attribute is not needed for committed images since the image query resolver automatically filters out any images committed to our system.

JIRA Issue: BA-606