Redis - Docker mod for any container

This mod adds redis to any container, to be installed/updated during container start.

In the docker arguments, set an environment variable DOCKER_MODS=linuxserver/mods:universal-redis

If adding multiple mods, enter them in an array separated by |, such as DOCKER_MODS=linuxserver/mods:universal-redis|linuxserver/mods:openssh-server-mod2