prune: allow having all prune options zero/missing

This is basically necessary for the GUI's prune widget, because we want to
pass along all options equal to zero when all the number fields are cleared.
And it's more similar to how it's done in PBS now.

Bumped the APIAGE and APIVER, in case some external plugin needs to adapt to
the now less restrictive schema for 'prune-backups'.

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>

PVE/Storage.pm

@@ -41,11 +41,11 @@ use PVE::Storage::DRBDPlugin;
 use PVE::Storage::PBSPlugin;
 
 # Storage API version. Increment it on changes in storage API interface.
-use constant APIVER => 7;
+use constant APIVER => 8;
 # Age is the number of versions we're backward compatible with.
 # This is like having 'current=APIVER' and age='APIAGE' in libtool,
 # see https://www.gnu.org/software/libtool/manual/html_node/Libtool-versioning.html
-use constant APIAGE => 6;
+use constant APIAGE => 7;
 
 # load standard plugins
 PVE::Storage::DirPlugin->register();