Publish to OpenVSX

[SableRaf]

Currently, the extension is published to the VS Code Marketplace through our release automation. To make it availableVS Code-compatible editors (like VSCodium, Theia, Cursor, etc.), we should extend this automation to also publish to OpenVSX submit a pull request to add it to extensions.json in the open-vsx/publish-extensions repo.

[SableRaf]

Looks like it is possible to tell OpenVSX to auto-publish based on the version in VS Code Marketplace: https://github.com/EclipseFdn/open-vsx.org/wiki/Auto-Publishing-Extensions