Need individual page metadata in SEO/link unfurl friendly formats

[mDuo13]

If you link any page on xrpl.org from Slack, social media, or other sites, you'll likely get a link preview individualized to that page, for example:

That's because Dactyl and the xrpl templates always populate various <meta> tags with details based on the page's title, "blurb", etc. Most of these can be set manually but it sets then to something reasonable if you don't (e.g. the blurb is based on the first paragraph).

The opensource site uses a generic description line for every page, for example:

With Redocly, you have to manually specify various seo frontmatter fields on the page for it to provide an individualized result. So we should make sure every page has the appropriate fields set and maybe even set up CI to request that those fields are set on each page if we can.