implement excludeFromBackup for volumes

@jan-eike.schnabel this MR now implements the option to exclude a volume from the backup system. Volumes that should be included in the backup get an excludeFromBackup: true label.

I will let you know if this has been implemented for the cosyna-opendap project

assigned to @philipp.sommer

mentioned in commit f2a16866

merged

mentioned in issue #1 (closed)

mentioned in merge request !24 (merged)