Publish extension to Open VSX Registry

[bjorkstromm]

It would be wise to also push this extension to Open VSX Registry so that it's available from Gitpod.

https://open-vsx.org/

[filiptronicek]

Currently, this is sadly not possible. The extension would need to switch to an OSS-licensed C# dependency, because currently it depends on ms-dotnettools.csharp [1]. One such alternative is https://github.com/muhammadsammy/free-omnisharp-vscode, which should be compatible with the extension as well.

cc @gep13