feat: Accept just image names

[nfebe]

Possibly only via the [UI[(https://github.com/flatrun/ui) or by both the UI and the agent, users should be able to deploy images from registries like docker hub or github container registry.

The agent will be responsible for generating a compose file using the image

[nfebe]

Partially implemented in: flatrun/ui#21

 Missing: Direct Image Deployment API

  There's no simple:
  POST /api/deployments
  {
    "name": "my-app",
    "image": "nginx:latest",
    "ports": [{"container": 80}]
  }

That would still eventually generate the compose relying on the UI is fragile