ci: Add change set checker workflow

[JayaShakthi97]

Purpose

This pull request introduces two new GitHub Actions workflows to automate the handling of pull requests and changeset checks. The workflows help ensure that each PR is properly tracked and validated for changesets, improving the release management process and compliance with versioning policies.

New GitHub Actions Workflows

• Added .github/workflows/receive-pr.yml to save the pull request number as an artifact when a PR is opened against the main branch, making it available for subsequent workflows.

Automated Changeset Validation

• Added .github/workflows/check-changeset.yml to automatically check for the presence and validity of changesets in PRs after the "Receive PR" workflow completes successfully.

Related Issues

• N/A

Related PRs

• N/A

Checklist

• Followed the CONTRIBUTING guidelines.
• Manual test round performed and verified.
• Documentation provided. (Add links if there are any)
• Unit tests provided. (Add links if there are any)

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines?
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets?

[JayaShakthi97]

Verified