Add Open VSX publishing for Cursor and other editors

[KyleKincer]

This PR adds support for publishing the extension to the Open VSX Registry, which is used by Cursor and other editors that support VS Code extensions.

Changes

• Added a new workflow file .github/workflows/publish-open-vsx.yml that publishes to Open VSX using the ovsx CLI tool
• Updated .github/workflows/publish_workflow.yml to include the Open VSX publishing step alongside the existing VS Code Marketplace publishing

Setup Required

To enable publishing, the repository maintainers will need to:

1. Create an account on Open VSX
2. Generate a Personal Access Token from the account settings
3. Add the token as a GitHub secret named OPEN_VSX_TOKEN in the repository settings

Once the secret is configured, the workflow will automatically publish new releases to Open VSX whenever changes are pushed to the main branch.

Benefits

• Makes the extension available to Cursor users

[KyleKincer]

@guillaume-kotulski any interest in this PR? Would be good to have, as a lot of our team is using Cursor. Let me know if I can help!