Request: Official Devcontainer Feature

The just feature listed on the [devcontainer Features list](https://containers.dev/features) is unofficial: https://github.com/guiyomh/features/tree/main/src/just

It would be great if an official one could be created.

Start by reviewing the devcontainer Features list and the linked unofficial implementation at github.com/guiyomh/features/tree/main/src/just. Determine the requirements for an official feature and its submission process; done means an official just feature is created and listed on containers.dev.

Written by the indexing model from the issue text.