GHA: Add post-release workflow

[rchlfryn]

Description

Adds a GitHub Actions workflow that automatically comments on issues and PRs when a release includes their fix, so contributors and reporters know which version contains their change.

Related Issues

Fixes #938

Key Changes

• Added .github/workflows/post-release.yml triggered on release: published events
• Uses apexskier/github-release-commenter@v1 to scan commits between releases and comment on associated issues/PRs

Why apexskier/github-release-commenter instead of Payload's fork?

This workflow was originally copied from Payload's post-release.yml, which uses a custom composite action (.github/actions/release-commenter) — a fork of the apexskier action with modifications for Payload's monorepo release process (tag filtering for non-linear multi-package releases, commenting on locked issues). Those features aren't relevant to us, and using the published action avoids maintaining a vendored copy of their fork.

How to test

1. Merge this PR
2. Create and publish a GitHub release
3. Verify that issues and PRs included in the release receive a comment like "🚀 This is included in version v1.0.0"

Future enhancements / Questions

• Could add label-template to automatically label released issues (e.g., released)
• Could add skip-label to exclude certain issues (e.g., dependency bumps) from being commented on

[github-actions]

Preview deployment: https://gha-post-release.preview.avy-fx.org

[github-actions]

🚀 This is included in version v1.8.0