fix: Improve docker example first user experience (#4972)

The base ubuntu image lands the user as root, but the terraform tempalte
expected /home/coder to be used. This change adds a user with the same
name as the Coder users username and allows them to sudo.

examples/templates/docker/build/Dockerfile

@@ -1,3 +1,18 @@
 FROM ubuntu
 
-RUN apt-get update && apt-get install -y curl wget git vim golang
+RUN apt-get update \
+	&& apt-get install -y \
+	curl \
+	git \
+	golang \
+	sudo \
+	vim \
+	wget \
+	&& rm -rf /var/lib/apt/lists/*
+
+ARG USER=coder
+RUN useradd --groups sudo --no-create-home ${USER} \
+	&& echo "${USER} ALL=(ALL) NOPASSWD:ALL" >/etc/sudoers.d/${USER} \
+	&& chmod 0440 /etc/sudoers.d/${USER}
+USER ${USER}
+WORKDIR /home/${USER}