Automate syncing blog posts from UW-UPL/harvest repo

[nicosalm]

Right now syncing blog posts from the harvest aggregator is a manual process:

1. git pull in UW-UPL/harvest to get the latest RSS/JSON updates
2. cp the files over to this repo
3. commit and push

This is annoying....

A solution may be to use repository_dispatch to trigger a rebuild when harvest updates.

• Add a workflow here that listens for a harvest_updated event
• Update harvest's GitHub Action to send that event after it updates the feed
• Change src/pages/blog.astro to fetch from harvest directly instead of using local files

Then harvest updates will automatically trigger a rebuild and the blog page stays fresh.

Can remove src/content/blogs/blog_posts.json and public/harvest/output/feed.xml after.

Docs: https://docs.github.com/en/actions/reference/workflows-and-actions/events-that-trigger-workflows#repository_dispatch