powermailpdf compatible with TYPO3 12

Make undkonsorten/powermailpdf with TYPO3 12 compatibility provided by vacando/powermail available as release for installing with composer.

This release will be removed as soon as (and if) undkonsorten/powermailpdf merges the open pull request and publishes an official release compatible with TYPO3 12.

{
    "repositories": [
        {
            "type": "git",
            "url": "https://github.com/jloderhose/powermailpdf.git"
        }
    ],
    "require": {
        "undkonsorten/powermailpdf": "dev-typo3v12"
    }
}