Add support for slug

Discussed in https://github.com/quarto-dev/quarto-cli/discussions/1408

^{Originally posted by sciwonder July 15, 2022}
I don't know if this is a feature currently (I searched but couldn't find any info on it), but is there a way to set up preferences for permalinks to things like blog posts in _metadata.yml in the posts folder? In my previous blog setup (using Hugo and Wowchemy), I had the following in config.yaml, for example:

permalinks:
  event: '/talk/:slug/'
  authors: '/author/:slug/'
  tags: '/tag/:slug/'
  categories: '/category/:slug/'
  publication_types: '/publication-type/:slug/'
  post: '/post/:year/:month/:day/:slug'

For blog posts, this translated to a hyperlink that started off with the year, followed by month, followed by day, and then the post's slug, which was specified within the post with slug: in the YAML header (e.g., //blog-name.netlify.app/post/2022/07/16/slug-for-blog-post/). Others might prefer a smaller hyperlink (e.g., '/post/:year/:slug') or even just the slug. I think setting this up in _metadata.yml might provide greater consistency. (Apologies if this feature already exists and I've just missed it in the documentation!)

Start with the linked Discussion 1408 and compare the requested Hugo/Wowchemy permalink patterns with Quarto's _metadata.yml and post YAML header examples. Done means the issue's requested configurable slug and permalink patterns are defined, implemented, and documented with examples for blog posts and related content types.