Consider Directory expansion

to follow-up on https://github.com/containers/olot/pull/131

we could implement a feature flag so that:
- by default passing a Directory as a parameter would throw error
- "force" so keep existing behaviour
- "expand" so that a directory is expanded in its constituent files

to have efficient layering for those edge cases.

Example, used in the build definitions as:

```sh
olot "${REMOVE_ORIGINALS_ARG[@]}" -m "$MODELCARD_PATH" "$TARGET_OCI" models/*
```

ref: https://github.com/konflux-ci/build-definitions/blob/3c7136732ac199914fc5fe78c0b037897e0b5a2c/task/modelcar-oci-ta/0.1/modelcar-oci-ta.yaml#L188

so the `models/*` is expanded to the model files, but also the 1st level directory.

With this feature, the directory contained in models/ would be more efficiently layered, by expanding on its constituent files.