Support for feed logos/icons for Follow

[danbao]

Clear and concise description of the problem

The inspiration for this comes from this ticket https://github.com/alexdebril/feed-io/issues/227

• Support for adding an icon/logo to an exported feed
• Support for consuming an icon/logo in an imported feed

More info here: https://snook.ca/archives/rss/add_logo_to_feed

Suggested solution

Atom

<feed>
   ...
   <icon>http://example.org/favicon.ico</icon> <!-- Must be a 1:1 image -->
   <logo>http://example.org/logo.jpg</logo><!-- Must be a 2:1 image -->
   ...
</feed>

RSS

<channel>
   ...
   <image>
    <!-- image size and description fields are optiona, see link above for moar infol-->
    <url>https://snook.ca/img/rss_banner.gif</url>
    <title>Snook.ca</title>
    <link>https://snook.ca/jonathan/</link>
    <width>111</width>
    <height>32</height>
    <description>Snook.ca features tips, tricks, and bookmarks on web development</description>
  </image>
  ...
</channel>

Alternative

No response

Additional context

No response

Validations

• [X] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.