added custom errors field to workflow schema
added custom errors field to workflow schema

4dn-dcic/fourfront,hms-dbmi/fourfront,hms-dbmi/fourfront,hms-dbmi/fourfront,4dn-dcic/fourfront,4dn-dcic/fourfront,4dn-dcic/fourfront,hms-dbmi/fourfront,hms-dbmi/fourfront