[REQUEST] add a link to AntennaPod

[juliaferraioli]

Is your feature request related to a problem? Please describe.
As a number of our listeners/readers use AntennaPod, we should add an easy link to it on the site.

Describe the solution you'd like
Add an entry in https://github.com/opensourcestories/opensourcestories.org/blob/main/data/podcasts.json for AntennaPod, pointing to https://antennapod.org/deeplink/subscribe?url=https://www.opensourcestories.org/stories/index.xml

Add an SVG to use for this entry in https://github.com/opensourcestories/opensourcestories.org/tree/main/layouts/partials/svg; suggested one from their brand repo: https://github.com/AntennaPod/Branding/blob/master/System%20Icon/system_icon_black.svg