Allow generating an empty metadata file

[IgnacioHeredia]

We can offer a functionality to generate an empty metadata file that is compliant with a given metadata version.

In my case, I want this for PAPI. When we fail to load the metadata of a module, I want to return an empty placeholder. Now I'm generating that placeholder manually.

metadata = {
    "metadata_version": "2.0.0",
    "title": "",
    "summary": "",
    "description": "",
    "doi": "",
    "license": "",
    "dates": {
        "created": "",
        "updated": "",
        },
    "links": {
        "documentation": "",
        "source_code": "",
        "docker_image": "",
        "ai4_template": "",
        "dataset": "",
        "weights": "",
        "citation": "",
        "base_model": "",
    },
    "tags": [],
    "tasks": [],
    "categories": [],
    "libraries": [],
    "data-type": [],
}