Add ability to customize the user/group for runtime

It would be ideal if users could update or specify the UID/GID for the user in the containers are runtime. While it is great that the images are not running as root, it would be ideal to be able to set the user at runtime. Other images handle the user creation at runtime through environment variables and some logic in the entrypoint script where it would manage ownership/permissions.

The use case is that `1000:1000` is typically the first non-root user on a linux system so being able to set it to a unique user would be ideal as my user has more access than any other user would.

Review the image entrypoint scripts and current non-root user setup, then determine how runtime UID/GID values and ownership handling should be exposed. Done means a container can accept a custom user and group at startup while retaining correct permissions; verify this by running an image with non-default values and checking its process and file ownership.

Written by the indexing model from the issue text.