v0.2.1

Race conditions during rolling releases

A few additional checks and fixes have been applied to fight possible race conditions during for instance a rolling
release of a Kubernetes StatefulSet when using the cache layer. Since it has no persistence, the Raft group formation
could get into state where Kubernetes had to kill one of the containers after a rolling release to get them healthy
again. This should now be fine as it was smooth like expected in the last tests.

Backups

The backups behavior has been changed slightly. It is still the case that only the current Raft leader will push the
backup to S3 storage (if configured), but each node will create an keep its own local backup. This helps when you don't
have S3 available and will make sure, that you will still have a backup "somewhere" even when you lose a full node.

Self-Healing

The self-healing tests have been simplified to make them easier to maintain in the future. They do not decide between
different folders being lost because you usually lose the whole volume or nothing at all. So if any issue comes up on
a Raft member node, the easiest solution is to simply delete the whole volume, restart and let it rebuild anyway.