Prevent need to move device.yml onto the device

### Description

As part of the [Device UX Review](https://github.com/flowforge/flowforge/issues/2427) I had highlighted that a pain point in the onboarding of a new device is actually the moving of the `yml` file from wherever your FF instance is running and getting it onto your device.

A much cleaner process here would be to be able to run commands directly from the device agent, pseudo example as follows:

```
flowforge-device-agent login
flowforge-device-agent connect
```

Following which the `connect` command would pull the `yml` and place it accordingly such that the device agent would work.