[Enhancement] Revamp VM and Volume Management

The [virtual_machine.py](https://github.com/frappe/press/blob/develop/press/press/doctype/virtual_machine/virtual_machine.py) became too large and tough to add new provider integration.

- Move the doctype to **infrastructure** module
- Refactor to have provider specific implementations (i.e vm.py, aws.py, hetzner.py)
- New provider integration should be easier also

Start with press/press/doctype/virtual_machine/virtual_machine.py and map its current VM and volume responsibilities. Move the doctype to the infrastructure module, then review the provider-specific separation requested for vm.py, aws.py, and hetzner.py. Done means the refactor supports easier addition of new provider integrations.

Written by the indexing model from the issue text.