Publish VS Code extension to Open VSX

[wackbyte]

Open VSX is an open-source alternative to the VS Code Marketplace that's used by some distributions of "Code - OSS" (the official open-source version of VS Code) and VSCodium. The ovsx tool publishes to Open VSX like vsce publishes to the VS Code Marketplace.

Publishing there would make the extension easily available to those who can't or don't want to use the proprietary Microsoft build of VS Code or its marketplace.