This patch adds a tab for cinder user messages for volume backups.
Cinder user messages show error details for cinder resources like if we
are unable to create a volume backup due to some failure in cinder it
will show us the reason for failure.
It also updates project and admin SnapshotDetailsTabs to use
DetailTabsGroup instead of TabGroup to improve top padding.
Also adds the fail_reason in the detail view, if backup errored.
Related-Bug https://bugs.launchpad.net/cinder/+bug/1978729
Change-Id: I4e639211043270e814fac489f915588af03f966a
20a571fdd2