Add Docker dev environment and initial code

Dockerfile.dev

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+FROM python:3.10
+
+# Install pipenv container-wide as root
+RUN pip install pipenv
+
+# Create unprivileged user with UID as specified by the build argument DEV_USER_UID, defaulting to 1000.
+# (This should match the UID of your local user. If it doesn't, use an ".env" file to overwrite this variable.)
+ARG DEV_USER_UID=1000
+RUN echo Creating dev user with UID $DEV_USER_UID && \
+    useradd -m -u $DEV_USER_UID dev
+USER dev
+
+## Create virtual environment using pipenv
+WORKDIR /app
+COPY Pipfile Pipfile.lock ./
+RUN pipenv install --dev --deploy
+
+# Set entrypoint to always run commands inside virtual environment
+ENTRYPOINT ["pipenv", "run"]
+
+# Set default command
+CMD ["bash"]