[plugin-registry] Use upstream openvsx image to get openvsx-server sources

[svor]

Is your task related to a problem? Please describe

Currently Che plugin registry uses a custom image to get openvsx-server sources. It was done because upstream version didn't work on our side. But after eclipse/openvsx#499 it should be possible to use the upstream version.

Describe the solution you'd like

We should update che plugin registry to use upstream openvsx server.

Also need to carefully test if the internal openvsx registry will work with the new image.

Describe alternatives you've considered

No response

Additional context

An initial work was started in eclipse-che/che-plugin-registry#1403