Updates to allow Bigboot to decrement from the default target size, down to a minimum threshold of 1GB

bigboot_setup_environment.yml

@@ -30,6 +30,7 @@
                 'bigboot_adjacent_lvm_device': bigboot_adjacent_lvm_device,
                 'bigboot_lv_shrink_size': bigboot_lv_shrink_size | int,
                 'bigboot_pv': bigboot_pv,
+                'bigboot_size_target': bigboot_size_target | int,
                 'ip_addresses': ansible_all_ipv4_addresses,
                 'server_hostname': ansible_hostname
               }