New file_mdm plugin created for extracting metadata from pdfs

Hello, this is just to inform you that I have created a new plugin extending file_mdm to extract metadata from pdfs:
https://www.drupal.org/project/file_mdm_pdf

Obviously derived heavily from the existing plugins, and uses smalot/pdfparser to extract the metadata.

A note on supported keys for PDFs - this can vary greatly from pdf to pdf as there are many extensions depending on authoring tools, or the purpose of the PDF, so once the pdf is loaded by the FileMetadataManager the supported keys array is populated for that specific PDF