[EC3-2437] Move optimizely-platform to Artifact Registry

[EshtiakAlam]

Summary

• Added GitHub Actions workflow to build and publish the optimizely-platform Python package to Google Artifact Registry on version tag pushes (v*.*.*)
• Replaced hard-coded version in setup.py with setuptools-scm to derive version automatically from git tags

Test plan

• Verify python -m setuptools_scm resolves version from git tags
• Verify python -m build produces sdist and wheel with correct version
• Push a test tag (v0.0.8) and confirm the workflow triggers and publishes to Artifact Registry
• Confirm existing package consumers are unaffected

[ahmedrafayat]

Missing: Publishing instructions

PR adds publish automation but no docs on how to use it. Please update the README:

Publishing a new version

1. Ensure all changes are merged to master
2. Go to Releases → Create a new release on GitHub
3. Create a new tag (e.g. v0.0.8) targeting master
4. Add release notes describing changes
5. Click Publish release
6. The GitHub Actions workflow will automatically build and publish to Google Artifact Registry

[ahmedrafayat]

All feedbacks were addressed. After merging this PR we will create a new release v0.0.8 (since 0.0.7 tag already exists).

LGTM!