Extract generateScheme() from the instance package into
common.GenerateScheme() and use it from both instance and
restore managers. The restore manager previously used a
hardcoded init() that ignored CUSTOM_CNPG_GROUP and
CUSTOM_CNPG_VERSION, causing restore jobs to fail when
running under a non-standard CNPG API group.
Signed-off-by: Marco Nenciarini <marco.nenciarini@enterprisedb.com>
