feat: Adds post-build hook.

[willum070]

This change would make Rube Goldberg proud! It does the following:

1. When a PR is merged, release workflow is triggered. It runs all the things including build-prod.
2. The build-prod script triggers a git hook (post-build.sh).
3. The post-build hook checks out dist, adds, creates a commit, and pushes to a dist branch on origin.
4. The dist-pr.yml workflow is triggered only on pushes to dist. If the actor is github-actions[bot], it creates, approves, and merges a PR with all of /dist changes, then deletes the branch.