add array of model support to compose provider commands

[glours]

Docker Model CLI can now support Compose configuration using one provider to declare all the models to pass to services at once using array like this:

  model_service:
   provider:
     type: model
     options:
       model:
         - ai/qwen2.5:latest
         - ai/smollm2:135M-Q2_K

We know check if the model is already downloaded before doing a pull.

If multiple models are passed the MODEL environment variable send to Compose will concat the model names using , like MODEL=ai/qwen2.5:latest,ai/smollm2:135M-Q2_K

[xenoscopic]

LGTM! It'll need a rebase on main, but the conflicts should be fairly painless.

[glours]

@xenoscopic done! 😉