[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

• Maintainers can manually trigger the workflow (via workflow_dispatch) to create a GitHub release. The workflow analyzes merged PRs since the last release, determines the version bump from semver labels (🔨 semver/patch, 🆕 semver/minor), and creates a release with auto-generated notes. Major releases (⚠️ semver/major) must still be created manually.

Test Plan

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

[simonjbeaumont]

I'm not sure we're ready for this one in this particular repo. We have a large compatibility suite that we run periodically, but is too large to run against pull requests, but we do use as signal before cutting a release.

[simonjbeaumont]

Result

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

Can we confirm if this is accurate. I don't think we want what's stated here. Although, it's not clear to me whether the PR actually does this.

[inductor]

@simonjbeaumont
Updated the PR comment. Sorry for responding late!