Replace with Valkey and Retire

[hairmare]

Valkey is the OSS future of Redis and this issue tracks the end-of-life of this container image.

Given that the container is currently based on https://github.com/sclorg/redis-container, our next step is to wait for Valkey availability on either sclorg or as a valkey-server RPM that is compatible with the currently used redis-server.

At the time of creating this issue, this describes a change in the far(-ish) future. After Valkey reaches stability, we expect it to get packages as an RPM for Fedora and, at a later stage, branched into EL. This can take a while and might involve a major bump at the OS level.

All in all, we don't use much Redis at RaBe. Apart from this container image there are only a few additional RPM based deployments. Currently our code base doesn't have a direct dependency on Redis but some systems we install contain 3rd party software with this dependency.