Get grants. This call describes the permissions assigned to the
specified entity that grant access to the specified
resource. Empty list is returned if no permissions are found for
the resource hrn provided regardless of the resource being present or not

Access Control:

• The calling principal must have either "listGrants" or "share" action permission for the resource "{resourceHrn}" in the "authorization" service.
• The realm of the calling principal MUST match the realm of the requested app.
• The calling principal MUST NOT include a project scope.