[Bug] Wikimedia script does not pull data for Public Domain images

[obulat]

Bug Description

Currently, we do not parse the license information for the Public Domain and PDM-marked image data from Wikimedia correctly, and therefore discard those images.
For CC-licensed images, imageinfo object has the following data:

"imageinfo": {
    "extmetadata": {
        "LicenseUrl": {
            "value": "https://creativecommons.org/licenses/by-sa/4.0",
            "source": "commons-desc-page",
            "hidden": ""
        },
        "LicenseShortName": {
            "value": "CC BY-SA 4.0",
            "source": "commons-desc-page",
            "hidden": ""
        },
        ...
    }
}

So, we use the following to get a license URL:

license_url = (
    image_info
        .get('extmetadata', {})
        .get('LicenseUrl', {})
        .get('value', '')
        .strip()
)

However, for Public Domain images, the LicenseUrl property has an empty value, so we discard the information for the image as invalid.
To fix this, we can use the LicenseShortName field to get correct data:

    if license_url == '':
        license_name = (
            image_info
                .get('extmetadata', {})
                .get('LicenseShortName', {})
                .get('value', '')
        )
        if license_name.lower() == 'public domain':
            license_info = licenses.get_license_info(license_='publicdomain', license_version='N/A')
        elif license_name.lower() == 'pdm-owner':
            license_info = licenses.get_license_info(license_='pdm', license_version='1.0')

Expected behavior

We expect that the information for Wikimedia Public Domain images is saved to the database.