[APIB-6718] Add SIMPLE org plan

Author: duane

xero_accounting.yaml

@@ -26823,6 +26823,7 @@ components:
           - IGNITE
           - GROW
           - COMPREHENSIVE
+          - SIMPLE
         Edition:  
           description: BUSINESS or PARTNER. Partner edition organisations are sold exclusively through accounting partners and have restricted functionality (e.g. no access to invoicing)  
           type: string