Feature Description:

Working with devcontainers has several advantages (isolation, consistent dev setup, security) and especially with the use of more autonomous AI agents, which we may want to allow invoking terminal commands, isolating the potential impact of those commands is crucial.

Therefore, I'd like to create a devcontainer setup to develop Theia, which I've started with #15662. It seems to work fine in VS Code, however, I ran into some issues when using it with Theia IDE.

First, the gitconfig mount doesn't seem to be supported. But even if I remove that, I get an error later down the road. Needs to be further investigated.