Undeploys gateway for the specified virtual network
All the required configuration to undeploy Azure gateway will be absorbed
as a part of request body in this API and gateway undeployment will be
triggered. Undeployment progress can be known from GetAzureGatewayStatus
API. Upon successful undeployment of a gateway, the deployment_step will be
UNDEPLOYMENT_SUCCESSFUL and gateway_status will be NOT_AVAILABLE. If any
error is encountered during undeployment, corresponding error_code and
error_message will be populated in gateway_instances_status