feat: GHA workflow to enforce changelog updates

[rjan90]

Add GitHub Actions workflow to enforce changelog updates:

• Add changelog.yml workflow that checks for CHANGELOG.md updates on PRs
• Support multiple skip options: label, PR title, or in PR description.
• Add changelog guidelines to README Contributing section

[rjan90]

Confirming that the check fails when there is no label on it:

[rjan90]

Once the label is added, the test passes:

[Copilot]

Pull Request Overview

Adds a GitHub Actions workflow to enforce changelog updates on pull requests to maintain better project documentation and change tracking.

• Creates a new workflow file that validates CHANGELOG.md updates on PRs
• Provides multiple skip mechanisms (label, PR title, or description patterns)
• Updates contributing guidelines in README with changelog requirements

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
.github/workflows/changelog.yml	New workflow to check for CHANGELOG.md updates with flexible skip options
README.md	Adds changelog guidelines to contributing section and fixes license links

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[rjan90]

We believe we can improve our habits around adding key items and breaking changes to the unreleased section of the changelog, and PR descriptions. I have therefore drafted this PR, and giving that approach a try for a while