Background images cache does not refresh on container start

[veteran29]

When Dockerfile is built application cache is created due to: https://github.com/ArmaForces/Website/blob/dev/.docker/Dockerfile#L100

When container on prod/dev env starts it does not warmup the cache again and due to that there's only one background image despite having correctly mounted volume with multiple background images. We need a way to build this cache at container startup.