OCI image spec annotations

[eitsupi]

At this time there are no arguments to add labels with the devcontainer build command, so labels cannot be set without writing them in the Dockerfile.
If an option to add labels is implemented in the CLI (devcontainers/cli#157), I would like to set labels.

[eitsupi]

/usr/local/etc/vscode-dev-containers/meta.env is also worth considering: it can be difficult to identify the images used in Codespaces, so it is useful to be able to identify versions, etc. from within the container.

https://github.com/devcontainers/features/blob/2af02c198adabacff30c400b0bfcad972ce5abcc/src/common-utils/bin/devcontainer-info

[eitsupi]

Related to devcontainers/features#359.