.stackblitz config for auto install extensions

[ShenQingchuan]

I'd like to suggest that providing a special config for stackblitz editor to auto install VSCode extensions (that listed in recommendation .vscode/extensions.json)

[jiashengguo]

Me too. I'm the creator of ZenStack, a full-stack toolkit that includes a DSL schema file. It has a VSCode extension for handling syntax highlighting and error checking for the schema.

We plan to add more example projects to our website using StackBlitz. It would be great for users who open the link with the ZenStack extension already installed.