Add mount args to some utils components

[schmidt-ai]

Closes #786.

Test plan:
TBD — do we have a good path for testing mounts?

[kiukchung]

Test plan: TBD — do we have a good path for testing mounts?

For components we typically test that the resulting AppDef is what we expect it to be. As an example for mounts take a look at https://github.com/pytorch/torchx/blob/main/torchx/components/test/dist_test.py#L17.

Functionally, since we reduce components to an AppDef, the tests for each scheduler implementation tests for whether mounts are respected correctly when we convert the AppDef into the respective scheduler job definitions. Here's an example with the kubernetes scheduler: https://github.com/pytorch/torchx/blob/main/torchx/schedulers/test/kubernetes_scheduler_test.py#L144