Revert "docker: Remove remnants of .env file configuration"

This reverts commit 359a856.
We can simply pass the '-o' / '--non-unique' argument instead.

Signed-off-by: Stephen Finucane <stephen@that.guru>

Author: stephenfin

tools/docker/Dockerfile

@@ -1,13 +1,16 @@
 FROM ghcr.io/getpatchwork/pyenv:latest
 
+ARG UID=1000
+ARG GID=1000
+
 ARG TZ="Australia/Canberra"
 ENV DEBIAN_FRONTEND noninteractive
 ENV PYTHONUNBUFFERED 1
 ENV PROJECT_HOME /home/patchwork/patchwork
 ENV DJANGO_SETTINGS_MODULE patchwork.settings.dev
 
-RUN groupadd patchwork && \
-    useradd --gid=patchwork --create-home patchwork
+RUN groupadd --gid=$GID patchwork && \
+    useradd --uid=$UID --gid=$GID --create-home patchwork
 RUN rm -f /etc/localtime; ln -s /usr/share/zoneinfo/$TZ /etc/localtime
 
 RUN eval "$(pyenv init -)"