Display cover image on subscribe page

**Short description**: Display a feed's cover image when cover image URL is provided in a parameter.

**Location**: Subscription page: https://antennapod.org/deeplink/subscribe/?url=https://podcast.thelinuxexp.com/@tlenewspodcast/feed.xml&title=Linux%20%26%20Open%20Source%20News
I would display it left from the page/podcast title.

**Why have this**: Makes the subscription page more appealing

**More info**:

* Builds on: https://github.com/AntennaPod/antennapod.github.io/pull/303
* Context: https://forum.antennapod.org/t/webplayer-share-landing-page-deeplink/3865
* Inspiration: https://podcastindex.org/podcast/5948837 / https://github.com/Podcastindex-org/web-ui/blob/d9b8e005a0c6ccfb86cd7dcff534fa86935fa9ac/ui/src/components/PodcastHeader/index.tsx#L94
* Need to check CORS. As noted by @ueen:
> CrossOriginResourceSharing would allow embedding images and audio. Whether this is supported by most podcasthosts is an open question that needs to be investigated.*
>
> *check this out [Podcastindex.org](https://podcastindex.org/podcast/1037491?episode=16729419694) image and audio doesnt seem to be cached, its linked straight from podigee-cdn

Nice to haves: display also 'author' and 'description'. On app side we need to consider [URL maximum length](https://www.baeldung.com/cs/max-url-length) handled by browsers - i.e. probably make the Description (stripped of any HTML) the last parameter and cut off at 2048 characters.