Related to #190.

With 5.9's release, we should begin seeing more and more "Site Building" patterns like Headers, Footers, and Query blocks. Especially as themes gain the ability to host patterns in the directory and reference them in their themes (WordPress/gutenberg#35364)

In Gutenberg, these will likely be pulled in contextually depending on the section of the site the user is editing. For example, if they're editing their header, Gutenberg can pull in featured header patterns from the directory. (WordPress/gutenberg#36697, WordPress/gutenberg#28739).

In the front-end Pattern directory, the purpose and appearance of these blocks is very different from the more general patterns in the directory. It'll be a bit awkward to show them interspersed amongst each other in the general "All" feed. We should consider figuring out a way to separate these out, so that folks can browse just Site Building patterns, or just General patterns.