Document whether replication is supported

[haslersn]

Hi! I'd like to know if it's supported to run multiple replicas of the roundcube container (given that they access the same database). My primary intention is high availability, but load-balancing would be a side-effect, too. however, I didn't find anything about this in the documentation.

If this is possible in principle, are there any directories that must be shared between the replicas? Does the configured temp_dir need to be a shared directory, or can every replica have its own temp_dir? I think this depends on whether specific files in the temp_dir are only used in a single php invocation or across multiple php invocations.