feat: Add support for indexing pdf's through the media module

This MR adds the ability to index media items with mime-type 'application/pdf'. Whenever a media items is detected and it has this mime-type, the Search API back-end will submit the document without content, it will provide a URL to the PDF document. This will trigger a crawl action from the Vragen.ai API, which will then index the PDF on the given URL.