Making docs file smaller by around 40% using multi-stage builds

{{cookiecutter.project_slug}}/compose/local/docs/Dockerfile

@@ -1,28 +1,58 @@
+FROM python:3.8-slim-buster as build_stage
+
+ENV PYTHONUNBUFFERED 1
+ENV PYTHONDONTWRITEBYTECODE 1
+
+# Requirements are installed here to ensure they will be cached.
+COPY ./requirements /requirements
+
+RUN apt-get update && apt-get install --no-install-recommends -y \
+    # dependencies for building Python packages
+    build-essential \
+    # psycopg2 dependencies
+    libpq-dev \
+    # Translations dependencies
+    gettext \
+    # Uncomment below lines to enable Sphinx output to latex and pdf
+    # texlive-latex-recommended \
+    # texlive-fonts-recommended \
+    # texlive-latex-extra \
+    # latexmk \
+    # cleaning up unused files
+    && apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false \
+    && rm -rf /var/lib/apt/lists/* \
+	# install python dependencies
+    && pip install --no-cache-dir --use-feature=2020-resolver -r /requirements/local.txt -r /requirements/production.txt \
+    && rm -rf /requirements
+
+
 FROM python:3.8-slim-buster
 
 ENV PYTHONUNBUFFERED 1
 ENV PYTHONDONTWRITEBYTECODE 1
 
-RUN apt-get update \
+
+RUN apt-get update && apt-get install --no-install-recommends -y \
     # dependencies for building Python packages
-    && apt-get install -y build-essential \
+    build-essential \
     # psycopg2 dependencies
-    && apt-get install -y libpq-dev \
+    libpq-dev \
     # Translations dependencies
-    && apt-get install -y gettext \
+    gettext \
     # Uncomment below lines to enable Sphinx output to latex and pdf
-    # && apt-get install -y texlive-latex-recommended \
-    # && apt-get install -y texlive-fonts-recommended \
-    # && apt-get install -y texlive-latex-extra \
-    # && apt-get install -y latexmk \
+    # texlive-latex-recommended \
+    # texlive-fonts-recommended \
+    # texlive-latex-extra \
+    # latexmk \
     # cleaning up unused files
     && apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false \
     && rm -rf /var/lib/apt/lists/*
 
-# Requirements are installed here to ensure they will be cached.
-COPY ./requirements /requirements
-# All imports needed for autodoc.
-RUN pip install -r /requirements/local.txt -r /requirements/production.txt
+
+# copy python dependencies from python-build-stage
+COPY --from=build_stage /usr/local/lib/python3.8/site-packages/ /usr/local/lib/python3.8/site-packages/
+COPY --from=build_stage /usr/local/bin/ /usr/local/bin/
+
 
 WORKDIR /docs