[Feature](elektra): Filter to show available/unused volumes

[edda]

Description We have a feature request to easily make it possible to see all unused volumes (state "available").

See here: https://github.wdf.sap.corp/PlusOne/enhancements/issues/117

Problem Statement Based on this info customers can easily identify capacity waste, check and decide on removal...

Proposed Solution

• Add a filter next to the searchbox named "Show only available" that filters the volume list to show only available volumes
• Show updated_at date in volume list