Support for other common formats

I recently migrated to Docspell from paperless-ngx and it's been pretty great so far. Unfortunately I'm running into one issue, which is that while Docspell can store my Powerpoint presentations, it can't index or display them. Paperless solved this using [Apache Tika](https://tika.apache.org/) as an optional extension so to speak, and this seems like something Docspell could do as well, especially since it is already designed to work with external services (Solr). I would love Tika (and by extension, more supported formats) to be integrated with Docspell, either as a core feature or an addon (and if such an addon exists I would appreciate a pointer to it - the addon system is a bit opaque to me).