'OpenShift: Delete Storage' command should not delete storage from tree until it is pushed

[dgolovin]

Latest odo release 'odo storage delete' removes storage from local context only and require to push it to propagate changes to cluster.
Current extension implementation works correctly only with previous odo release, where storage would be deleted directly in cluster.

'OpenShift: Delete Storage' command should be changed to ask about pushing changes to the cluster.

[mohitsuman]

Reference upstream issue: redhat-developer/odo#2793