Offline che-plugin-registry build fails to embed all vsix files for plugins with depedencies

[ericwill]

Describe the bug

Che version

• latest
• nightly
• other: please specify

Steps to reproduce

1. Build the che-plugin-registry with the offline parameter: build.sh --offline.
2. When the build finishes, enter the container to inspect the generated meta.yaml files.
3. Find the meta.yaml for a plugin that has dependencies, i.e. the ``metaYaml -> extraDependencies` field
4. Look at the extensions field and observe that the 2nd and onward extensions are not relative: links but are regular HTTP URLs.

For example, the node-debug2 plugin meta.yaml:

apiVersion: v2
publisher: ms-vscode
name: node-debug2
version: latest
type: VS Code extension
displayName: Node Debug
title: Node Debug
description: Node.js debugging support
icon: /v3/images/ms-vscode-node-debug2-icon.png
category: Debuggers
repository: 'https://github.com/Microsoft/vscode-node-debug2.git'
firstPublicationDate: '2020-10-07'
latestUpdateDate: '2021-05-04'
spec:
  containers:
    - image: 'quay.io/eclipse/che-plugin-sidecar@sha256:4bce2e39fee6b9e4a8b4e8681380ce2462674597a48b81c131cbbf055dd5d0c3'
      name: vscode-node-debug
      memoryLimit: 512Mi
      cpuRequest: 30m
      cpuLimit: 500m
      env:
        - name: CHE_THEIA_SIDECAR_PREFERENCES
          value: '{"debug.node.useV3":false}'
  extensions:
    - 'relative:extension/resources/open-vsx_org/api/ms-vscode/node-debug2/1_42_5/file/ms-vscode.node-debug2-1.42.5.vsix'
    - 'https://open-vsx.org/api/ms-vscode/node-debug/1.44.8/file/ms-vscode.node-debug-1.44.8.vsix'

Expected behavior

All links in the extensions field should be relative: when building with the offline parameter.

Runtime

• kubernetes (include output of kubectl version)
• Openshift (include output of oc version)
• minikube (include output of minikube version and kubectl version)
• minishift (include output of minishift version and oc version)
• docker-desktop + K8S (include output of docker version and kubectl version)
• other: N/A

Screenshots

Installation method

• chectl
  • provide a full command that was used to deploy Eclipse Che (including the output)
  • provide an output of chectl version command
• OperatorHub
• N/A

Environment

• my computer
  • Windows
  • Linux
  • macOS
• Cloud
  • Amazon
  • Azure
  • GCE
  • other (please specify)
• Dev Sandbox (workspaces.openshift.com)
• other: please specify

Eclipse Che Logs

Additional context

[ericwill]

Fixed by eclipse-che/che-plugin-registry#953