add docker compose for backend

Dockerfile

+FROM python:3.8
+WORKDIR /var/www/oser-backend
+COPY . .
+VOLUME [ "/var/www/oser-backend" ]
+ENV DEBIAN_FRONTEND=noninteractive 
+RUN apt update && apt install -y build-essential postgresql libpq-dev python3-dev git
+RUN python3 -m pip install -r requirements.txt
+EXPOSE 8000
+CMD python3 manage.py makemigrations && python3 manage.py migrate && python3 manage.py runserver 0.0.0.0:8000