Separate VS Code user-dir per image

[DeepCowProductions]

Is your feature request related to a problem? Please describe. VS Code extensions are global per user, same as every other global setting inside the container.

Describe the solution you'd like A separate VS Code home per image.

Additional context Steps to achieve this:

• [x] set VS Code --user-dir flag to $HOME/.local/code-server/$IMAGE_NAME for the code server.
• [x] extend/fork vscode-server-proxy to enable this.
• [x] preload some extensions per image - add install script to every image, to install them into $HOME/.local/code-server/$IMAGE_NAME (if the workspace is new) now done with vscode builtin extensions

[DeepCowProductions]

Prototype is working under develop.