Add init script to load keys

Add new init scripts which allow automatic loading of keys if
keylocation property is set to a URI.

Reviewed-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Benedikt Neuffer <ogelpre@itfriend.de>
Closes #11659
Closes #11662

rpm/generic/zfs.spec.in

@@ -424,6 +424,7 @@ fi
 %else
 if [ -x /sbin/chkconfig ]; then
     /sbin/chkconfig --add zfs-import
+    /sbin/chkconfig --add zfs-load-key
     /sbin/chkconfig --add zfs-mount
     /sbin/chkconfig --add zfs-share
     /sbin/chkconfig --add zfs-zed
@@ -454,6 +455,7 @@ fi
 %else
 if [ "$1" = "0" -o "$1" = "remove" ] && [ -x /sbin/chkconfig ]; then
     /sbin/chkconfig --del zfs-import
+    /sbin/chkconfig --del zfs-load-key
     /sbin/chkconfig --del zfs-mount
     /sbin/chkconfig --del zfs-share
     /sbin/chkconfig --del zfs-zed