Disable Redis persistence

[willroberts]

Summary

Our Redis data is transient, so this helps reduce resource utilization and log spam.

Infrastructure changes (.github/, terraform/, etc.):

• Adds support for custom commands in ECS tasks
• Uses custom commands to disable Redis persistence

Testing

Have you have tested your changes in the following scenarios? Feel free to check off scenarios which don't apply.

• [x] Starting backend services locally with docker compose up succeeds.
• [x] I am able to create a new user and log in locally.
• [x] I am able to complete a practice game locally.
• [x] I am able to complete a purchase of Orbs, etc.