Provides OpenVSX CheCluster URL to user containers

[benoitf]

Is your task related to a problem? Please describe

Part of https://github.com/eclipse/che/issues/20549 Plugin-Registry will include an OpenVSX instance. Admin will have a choice to say to either use 'OpenVSX.org' or 'plugin-registry OpenVSX' with the CheCluster https://github.com/eclipse/che/issues/21598

And then, CheCode(our VS Code) needs to know when booting if registry needs to be OpenVSX.org or another URL https://github.com/che-incubator/che-code/pull/85

But to know what to do, CheCode needs to get the value specified in the CheCluster CR but a user container has no access to the CheCluster object, so it's the Dashboard that needs to propagate this information

Describe the solution you'd like

depends on https://github.com/eclipse/che/issues/21598 Adds OPENVSX_URL with value coming from components.devWorkspace.cheServer.pluginRegistry.OpenVSXURL

Describe alternatives you've considered

No response

Additional context

No response

[l0rd]

I would use OPENVSX_REGISTRY_URL as the name of the env variable. Added the comment to the CheCluster issue too.