Fix git's `detected dubious ownership in repository` warning

[lsorber]

Problem description and solution: https://www.kenmuse.com/blog/avoiding-dubious-ownership-in-dev-containers/

[lukin0110]

I'd add this somewhere in the Dockerfile instead of in the devcontainer.json and use system instead of global:

RUN  git config --system --add safe.directory '*'

Reasons:

• Adding it to the Dockerfile will solve the issue in a central place. It will also solve the same issue when the image is used on linux outside a devcontainer/VSCode/codespaces context. Eg: docker compose run dev
• Using system will add the config to /etc/gitconfig. In case global is used it will be added to ~/.gitconfig. But this will make VSCode fail to share gitconfig / credentials.