Upgrade check is used to find updates for the current cluster.
Optionally the found upgrades can be persisted to the config
for consumption by the upgrade-execute cmd.
The old `upgrade execute` in this commit does not work with
the new `upgrade plan`.
The current versions are read from the cluster.
Supported versions are read from the cli and the versionsapi.
Adds a new config field MicroserviceVersion that will be used
by `upgrade execute` to update the service versions.
The field is optional until 2.7
A deprecation warning for the upgrade key is printed during
config validation.
Kubernetes versions now specify the patch version to make it
explicit for users if an upgrade changes the k8s version.
Version validation checks that the configured versions
are not more than one minor version below the CLI's version.
The validation can be disabled using --force.
This is necessary for now during development as the CLI
does not have a prerelease version, as our images do.
