AutoMembershipPrincipals.getAutoMembership must resolved inherited groups

while testing OAK-9803 i noticed that ExternalGroupPrincipalProvider#getMembershipPrincipals and ExternalGroupPrincipalProvider#getPrincipals do not included groups inherited from configured auto-membership groups:

if group 'a' is configured as automembership and is in turn member of 'b', 'b' must also be part of the complete set of principals return by either methods.