github: add GitHub API function to submit pull request reviews

[nvsriram]

Summary

This PR introduces a new GitHub API function that enables Plaid modules to submit a review on a pull request.

Changes

• STL: Added PullRequestReviewEvent enum, SubmitPullRequestReviewRequest struct, submit_pull_request_review, and approve_pull_request wrapper in runtime/plaid-stl/src/github/pull_request.rs.
• Runtime: Implemented submit_pull_request_review method in the GitHub API handler in runtime/plaid/src/apis/github/pull_requests.rs
• Validation: Added validate_review_body in runtime/plaid/src/apis/github/validators.rs to ensure non-empty body is provided when event is RequestChanges or Comment
• Function Registration: Added function mapping and implementation in runtime/plaid/src/functions/api.rs

Rationale

This functionality is needed to enable automated approval of pull requests from Plaid modules. The implementation uses the GitHub Pull Request Reviews API endpoint /repos/{owner}/{repo}/pulls/{number}/reviews with caller-specified event and body.

[michelemin]

Looks good! I would expand the API a bit and double check the POST body. Then we can ship it 🙂

[Copilot]

Pull request overview

This PR adds a new GitHub API capability to Plaid so modules can approve a pull request by creating a PR review with the APPROVE event via GitHub’s Pull Request Reviews REST API.

Changes:

• Added ApprovePullRequestRequest plus a new approve_pull_request(...) STL helper to call the host function and return the created review JSON.
• Implemented the runtime GitHub API handler method that POSTs to /repos/{owner}/{repo}/pulls/{number}/reviews with event: "APPROVE" (and optional body).
• Registered the new host function and mapped "github_approve_pull_request" to the runtime implementation.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
runtime/plaid/src/functions/api.rs	Registers and exposes the new github_approve_pull_request host function to modules.
runtime/plaid/src/apis/github/pull_requests.rs	Implements the runtime POST call to create an approval review for a PR.
runtime/plaid-stl/src/github/pull_request.rs	Adds request struct + STL wrapper function for approving PRs and returning raw JSON.

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[michelemin]

LGTM!