Feed plugin: Add options info.image, info.icon and info.color

[castaneai]

Description

Add option to add custom fields to RSS feed output. This can be used as extended metadata for Feedly, for example.

refs:

• https://devhd.wordpress.com/2015/07/31/10-ways-to-optimize-your-feed-for-feedly/
• https://justingarrison.com/blog/2022-11-22-hugo-rss-improvements/
• https://github.com/withastro/astro/tree/main/packages/astro-rss#customdata

Related Issues

Check List

• Have you read the
  CODE OF CONDUCT
• Have you read the document
  CONTRIBUTING
  • One pull request per feature. If you want to do more than one thing,
    send multiple pull request.
  • Write tests.
  • Run deno fmt to fix the code format before commit.
  • Document any change in the CHANGELOG.md.

[oscarotero]

I'm okay with adding support for Feedly, but I'd rather to have good defaults instead of adding manually these fields.
What do you think about the following changes?

• Add xmlns:webfeeds="http://webfeeds.org/rss/1.0" and `version="2.0" to the XML. No need to configure it.
• Extend the FeedInfoOptions interface with color, image and icon properties. This also matches with Metas plugin that have these properties.
• Some of these properties are also supported by JSON Feed, (like icon for example), so we should modify the JSON generation to use them.

[castaneai]

Thanks, @oscarotero.
That change sounds like a good one! I'm willing to take a little time to adopt those changes.

[oscarotero]

Great! Thank you!

[castaneai]

I have rewritten it to three options: image, icon and color.

[oscarotero]

It's perfect. Thank you!