Changes to List custom measure field mappings for an account

removed the required property mappings from the response with the 200 status

api operation id FetchCustomFieldMappings removed and replaced with ListCustomFieldMappings

added the new optional query request parameter pageSize

added the new optional query request parameter pageToken

added the required property items to the response with the 200 status

added the required property meta to the response with the 200 status

endpoint added