Handle removal of etcd.initialClusterState during helm upgrade in upgrade-job

[niladrih]

Ref: openebs/mayastor-extensions#536

The upgrade-job, as of 2.7.0 reuses all of the existing helm values from the source chart. The removal of the parameter from the values.yaml would mean that during upgrade that value has to be forcibly removed when moving to 2.7.0+ versions. This needs to be handled somehow.

If there is no new design changes to upgrade, a new entry to the helm::values.rs module is required which explicitly removes the value from the values set. This might also be required even if helm's --reset-then-reuse-values flag is used, as previous upgrade-jobs would have used the -f values.yaml option during upgrade and would have explicitly set ALL of the source chart's values (and they would be now visible on helm get values output).