chore(ci): Add round-robin reviewer auto-assignment

[jiayuasu]

Automatically assigns one reviewer per PR in round-robin from the list in .github/reviewers.json.

How it works:

• assign-reviewer.yml (triggered by pull_request) captures PR number and author into an artifact
• assign-reviewer-write.yml (triggered by workflow_run) reads the artifact, loads the reviewer list from the trusted main branch, computes the round-robin pick, and assigns the reviewer

This follows the ASF-recommended pull_request + workflow_run split pattern to safely handle fork PRs without using pull_request_target. See ASF GitHub Actions Security.

To update the reviewer list, edit .github/reviewers.json — no workflow changes needed.

[jiayuasu]

@paleolimbot This is to enable (approx.) round-robin PR review assignment on SedonaDB.

[Copilot]

Pull request overview

Adds a secure GitHub Actions-based automation to request one reviewer per newly opened PR using a deterministic round-robin selection from a repo-managed list, implemented via the ASF-recommended pull_request + workflow_run split to support fork PRs safely.

Changes:

• Introduces a pull_request workflow that captures PR metadata and uploads it as an artifact.
• Introduces a workflow_run workflow (with write permissions) that reads the artifact, loads reviewers from main, computes the assignee, and requests a review.
• Adds .github/reviewers.json as the single source of truth for the reviewer pool.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
.github/workflows/assign-reviewer.yml	Captures PR number/author on PR open and uploads metadata artifact.
.github/workflows/assign-reviewer-write.yml	Downloads metadata from the prior run, reads trusted reviewer config from main, and requests a reviewer.
.github/reviewers.json	Defines the reviewer rotation list used by the assignment workflow.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[paleolimbot]

Happy to give this a try!