Full Data Export

### What problem does this address?

I loved the End of Year feature (#410) but it left me with more questions about my Pocket Casts habits. I know you can export your subscriptions, and that there are stats for total days listened and days saved, but I would like even more.

(Side note: I'm an American, but I feel like this is something that sometimes goes hand in hand with [GDPR Data Portability](https://gdpr.eu/data-privacy/) requirements.)

### What is your proposed solution?

An additional export option for outputting JSON/XML/CSV of all listening data available.

### Did you search for existing feature suggestions?

- [X] I have searched for existing feature suggestions.

The issue does not name files, tests, or entry points. Begin by locating the existing subscription export and listening-statistics paths, then determine which listening data is available for export and how an additional export option should expose it in JSON, XML, and CSV; done means users can export the requested data in all three formats.

Written by the indexing model from the issue text.