Publish updates to Open VSX Registry

[mettekou]

Is your feature request related to a problem? Please describe.
I cannot automatically update the Vitest extension from VSCodium.

Describe the solution you'd like
Publish each update to the Vitest extension to the Open VSX Registry, so VSCodium users can access it.

Describe alternatives you've considered
Manually installing the Vitest extension from the Visual Studio Marketplace every time it is updated.

Additional context
See #43, which was closed without providing a structural solution to the problem.

[mmailaender]

Same for GitPod. Not sure if you already aware: There is a GitHub Action to automate the publishing process to VSX @zxch3n https://github.com/HaaLeo/publish-vscode-extension#readme