Add a builder user and install sudo (#40)

* Add a builder user and run everything as it

This should allow to also build PKGBUILDs with makepkg which isn't
allowed to run as root.

* Only create the user, don't run as it by default

GitHub Actions run the checkout modules as a separate user which breaks
if the Docker container defines its own user.

Author: rnestler

Dockerfile

@@ -1,8 +1,12 @@
 FROM archlinux:latest
-RUN pacman --noconfirm -Sy rustup gcc pkg-config \
+RUN pacman --noconfirm -Sy rustup gcc pkg-config sudo \
     && rm /var/lib/pacman/sync/* \
     && rm /var/cache/pacman/pkg/*
 
+# Add a builder user since makepkg cannot (and should not) be run as root
+RUN  useradd -m builder \
+  && echo "builder ALL=(ALL) NOPASSWD: ALL" > /etc/sudoers.d/builder
+
 ARG RUST_VERSION=stable
 RUN rustup install --profile minimal $RUST_VERSION