Add <podcast:transcript> tags to podcast feeds

[ScottDeLuzio]

It would be helpful if the <podcast:transcript> tags (as described here https://rss-extension.buzzsprout.com/1.0/podcast/) could be added to podcast feeds. It could be added as a feature to Seriously Simple Transcripts where there is an input field for SRT, JSON and HTML transcripts that could be uploaded to each episode. If those files exist for an episode, then they could be added to the <item> tag in the podcast feed. However, in order for that to happen, I think the podcast feed file (seriously-simple-podcasting/templates/feed/feed-item.php) should have a do_action() function somewhere inside the <item> tag (something like do_action( 'ssp_add_to_feed_item', get_the_ID() ); should work). This will allow the Seriously Simple Transcripts plugin to hook into the feed to add this data. It also will allow other developers to add their own data to the feed should the need arise in the future. That way even if you don't add the feature to SST, developers could add it themselves.