Configure devcontainer to use same uid/gid as docker base

[relud]

While investigating issues related to docker/for-mac#6734 (comment), I found that in docker desktop for mac the mounted volume is retaining file ownership permissions between the test and devcontainer volume mounts.

For example, if vscode starts a devcontainer first, I open a terminal in vscode and run ls -lha, I might see that /app is owned by vscode:vscode, but if I then run docker compose run --rm test bash and in that container run ls -lha the files are owned by 1000:1000 because vscode isn't a user/group in the test container. File ownership then remains sticky for some unknown amount period after that.

This treats the problem by explicitly defining the app user/group in devcontainer with the same ids used in the test container.

[relud]

@biancadanforth with this patch, i then run chown -R app:app /app from vscode in the devcontainer (it throws exceptions on some git read-only objects that are already owned by app:app, so that's fine), and after that make lint works with VirtioFS.

[biancadanforth]

TIL: Paraphrasing from relud: On Mac, the Docker host is a VM, and that hides the original file permissions of the /app directory. Since test and devcontainer both mount $PWD/app from the same VM, using chown in one applies to the VM filesystem (including the other container). Also on Mac, the default user/group id for VS Code's Dev Containers is 1000 instead of trying to match the user id/ group id of the host machine (what Linux VS Code Dev Containers does).

[smarnach]

Thanks for the fix! I thought the permissions were only an issue on Linux, and since it worked fine for me, I kept it as simple as possible.

[smarnach]

Unfortunately, this broke the dec container build for me:

 > [devcontainer dev_container_auto_added_stage_label 3/6] RUN groupadd --gid 1000 app &&     useradd -g app --uid 1000 --shell /usr/sbin/nologin --create-home app &&     chown app:app /app/:
0.402 groupadd: GID '1000' already exists

This is probably because my uid happens to be 1000. I'll figure out how to solve this after lunch.