Publish Podcast to index

Is your feature request related to a problem? Please describe

I would like my podcast to show up on the map and found a bit better. Therefore, I would like to know where and how I can publish it. This means that there are certain standards that get used and that are compatible with the ways castopod provides an API and platforms. One example is ActivityPub. But I would also like to publish it to https://podcastindex.org/add

Describe the solution you'd like

At the bottom of editing a podcast, I would like to have a list of podcast platforms that use the XML feed: https://pod.foss.wales/cp-admin/podcasts/2/edit

Publish on podcastindex.org: You can publish the XML feed URL [URL follows] at https://podcastindex.org/add. [BUTTON: check if it is published]

When you press the button, then it should go green and say "published" or red "not published".

Describe alternatives you've considered

It is nice for people to be led into these things where they are. I think, documentation would be nice but it is a bit hard to find. If this was in a documentation, it would probably be a page like this:

Published your first podcast? Now see what you can do with it!

Additional context

See https://toot.wales/@Castopod@podlibre.social/112603131246215355