Updated the operation id for Billing spec (#5727)

* Added specs for Agreements API in version 2018-11-01-preview

Added specs for Agreements API in version 2018-11-01-preview

* Updated as per naming convension

Updated as per naming convension

* Corrected specs and examples for BillingRP

Corrected specs and examples for BillingRP

* Fixed the errors

Fixed the errors

* Fixing errors in spec

Fixing errors in spec

* Updated examples

Updated examples

* Incorporated review comments

Incorporated review comments

* Incorporated review comments

* Incorporated review comments

Incorporated review comments

* Updated the operation id for Billing spec

Updated the operation id for Billing spec

* Incorporated review comments

Incorporated review comments

* Incorporated review comments

Incorporated review comments

* Fixed the errors

Fixed the errors

* Added multiple inputs

Added multiple inputs

* Fixed build errors

Fixed build errors

* Incorporated review comments

Incorporated review comments

* Incorporated review comments