[CI] Add automated release workflow using swift-temporal-sdk

[inductor]

Integrate swift-temporal-sdk's reusable auto-release workflow for automated semantic versioning releases. Update CONTRIBUTING.md with a link to the workflow documentation.

Motivation

• Automate the release process using semantic versioning labels, reducing manual overhead and ensuring consistent versioning across releases.

Modifications

• Add .github/workflows/auto-release.yml that uses swift-temporal-sdk's reusable workflow
• Update CONTRIBUTING.md with automated release process documentation linking to swift-temporal-sdk's workflow README

Result

• When PRs are merged with semver labels (semver/patch, semver/minor), the workflow automatically creates GitHub releases. Major releases require manual creation.

Test Plan

• Workflow will be validated after merge by labeling PRs with semver labels and verifying that releases are created automatically.

[czechboy0]

Thanks, @inductor! 🙏