`list` operations design

I noticed we have a [`list`](https://github.com/Azure/magic-module-specs/blob/master/batchapplication/api.yaml#L181) operation in batchapplication. I would like to name it as `list_by_parent` based on the following assumptions:

1. A top level (or maybe sub-resource as well) resource could be listed by resource group, we have `list_by_resource_group` support.
2. A sub-resource could be listed by its parent resource (e.g. batchaccount is batchapplication's parent), I would like to introduce `list_by_parent` to `api.yaml` for each sub-resource.

Correct me if you know there are other cases for this scenario.

If ALL sub-resources are not able to be listed by resource group, actually we might also combine those two into one `list_by_parent`, because we can treat `resource_group` as the parent of all top-level resources.