Context:
In order to implement resumable upgrades completed upgrade steps need to be recorded so the upgrade state can be picked-up later on.

AT:

• the progress of an upgrade/completed steps are recorded
• the state of the upgrade can be read on reexecuting the upgrade
• the progress must be stored in a way that does not depend on the machine the upgrade was run from (to allow resuming the upgrade from any machine with access to elasticsearch regardless of where a previous upgrade was started from) => ideally the state is stored in elasticsearch