Update docker containers to run as non-root user

[fyliu]

Overview

We need to make the Docker containers run as unprivileged user for better security and to resolve a migration files permissions issue for Linux users. Running as root user in the container means it'll create new migration files as root of the host as well, making it unreadable for the normal user until it's chmodded.

Action Items

• modify Dockerfile to run as normal user
• modify docker-compose file to run as normal user
• add documentation

Resources/Instructions

• app/Dockerfile
• docker-compose.yml