✨ feat: add support for social media cards

[welpo]

Summary

This PR introduces a new social_media_card setting so that links shared on social media sites have an image preview. Like this:

Changes

1. New social_media_card Setting:

   • Can be configured in config.toml, section front matter, and page front matter.
   • Hierarchy for setting value: page > section > config.

2. Cache Busting:

   • Cache busting implemented for social_media_card URLs to ensure social media sites fetch the latest image.

3. Social Media Cards Added:

   • Social media card images added to all posts and sections in the theme.

4. Documentation Updates:

   • Updated config.toml and theme.toml documentation with comments explaining the new social_media_card setting.

5. HTML Tag Fixes:

   • Corrected some HTML tags related to social media to ensure proper rendering.

6. Macro Updates:

   • Modified the hierarchy macro to handle non-boolean values, such as the new social_media_card setting.

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How to automate the creation of social media cards

I created all the cards running one command. For those interested in how I automated the creation of the social media card images, check out my blog post: From Bashful to Social Butterfly: Automating Link Previews for Zola Sites. There I explain how I created the script I used to create these images (and automate their creation).

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Example

Here's one of the automatically generated social media cards, which will be shown as a preview when the post is shared on social media (Telegram, LinkedIn, Mastodon, Twitter…):