Populate vscode specific configurations

The devcontainer spec has a [section](https://containers.dev/supporting#visual-studio-code) that covers the support of VS Code specific properties. I am not sure how reasonable the `customizations.vscode.settings` are for the remote since those are stored in a local user session. (In the case of coder could be in a different volume). This might actually be a better issue for them to solve on that side then. If that is your opinion please feel free to close this issue and I will move it to the coder project.

Start with the linked VS Code-specific section of the devcontainer specification and inspect how Envbuilder currently handles devcontainer properties. Determine whether customizations.vscode.settings belong in Envbuilder or should be handled by the Coder project; the issue is done only once that ownership and the supported configuration scope are decided.

索引モデルが issue の本文から書いたものです。