Move ispconfig configuration into etcd
At the moment ISPconfig has all its configuration in a mysql database. MySQL by itself doesn't provide built in distribution of data to different nodes. I propose therefore to migrate over time the database over to https://etcd.io/ which would make it easier to build clustered ispconfig set-ups.
Etcd is used by many other systems like e.g. Kubernetes for storing its configuration. An added benefit of etcd would be the possibility to track configuration changes: https://etcd.io/docs/v3.4.0/dev-guide/interacting_v3/#read-past-version-of-keys