[Discussion] Workflow rollback support

[qiankunli]

in my case, i want to use goflow to create some resources on a public cloud. like creating a cloud vm with public ip.

1. create a vm using cloud openapi
2. wait the status of vm is running
3. create a public ip using cloud openapi
4. wait the status of public ip is available
5. bind the public ip with vm
6. other steps

i want

1. if I cancel the workflow(like run flow.cancel()), workflow can free the created resources(vm,public ip etc)
2. if one step failed, workflow can free the created resources(vm,public ip etc)