Added 'KEEP_DEPENDENCIES' Docker argument

As per #1817, tox is missing build dependencies and cannot run tests
in containers. This commit added an argument to make purging packages
optional, allowing to optimize image for deployment, while also
keeping the required packages in dev environments.

Dockerfile

@@ -1,6 +1,9 @@
 # pull official base image
 FROM python:3.12-slim-bookworm
 
+# Overridden in docker-compose.yml to fix tox in Docker
+ARG KEEP_DEPENDENCIES=False
+
 # set work directory
 WORKDIR /usr/src/app
 
@@ -34,11 +37,13 @@ RUN apt-get update \
         libpq-dev \
         zlib1g-dev \
     && python3 -m pip install --no-cache-dir -r ${REQ_FILE} \
-    && apt-get purge --assume-yes --auto-remove \
+    && if [ "${KEEP_DEPENDENCIES}" = "True" ]; then \
+        apt-get purge --assume-yes --auto-remove \
         gcc \
         libc6-dev \
         libpq-dev \
-        zlib1g-dev \
+        zlib1g-dev; \
+        fi \
     && rm -rf /var/lib/apt/lists/*
 
 # install node dependencies

docker-compose.yml

@@ -5,6 +5,7 @@ services:
             dockerfile: Dockerfile
             args:
                 - REQ_FILE=requirements/tests.txt
+                - KEEP_DEPENDENCIES=True
         entrypoint: ./docker-entrypoint.dev.sh
         command: python manage.py runserver 0.0.0.0:8000
         volumes: