Feature Request: Ability to move gPodder Folder to flatpak folder.

Gpodder has an environment variable that allows setting the home and download folder. It would be great if the flatpak could set these variables to a folder inside the flatpak home folder. Would help keep things neater in the user's home folder.

There's more information on the variables here:

https://gpodder.github.io/docs/user-manual.html#gpodder-home-folder-and-download-location

Start with the linked gPodder documentation on the home-folder and download-location environment variables, then inspect the repository's Flatpak configuration to determine where those variables can be set. Done means the Flatpak keeps gPodder's home and download folders inside its Flatpak home folder and the behavior is verified; no specific file or test is named.

Written by the indexing model from the issue text.