CodeGen from PR 17451 in Azure/azure-rest-api-specs

Fixing billing RP promotions S360 swagger issues  (#17451)

* Adding 2020-09-Preview same as 11-preview

* fixing lint issue

* fixing model

* fixing model

* fixing model

* pretify fix

* fixing linting

* more linting fix

* fixing swagger correctness

* Fixing swagger

* fixing swagger

* Adding operations API

* fixing validation error

* fixing version param

* Fixing the operations API

* fixing missing reference

* fixing swagger model

* fixing object type

* fixing more swagge validations

* removing operations

* removing operations

* fixing model

* fixing path

* fxing swagger