feat : use --no-cache-dir flag to pip in dockerfiles to save space

using the "--no-cache-dir" flag in pip install, make sure downloaded packages
by pip don't cache on the system. This is a best practice that makes sure
to fetch from a repo instead of using a local cached one. Further, in the case
of Docker Containers, by restricting caching, we can reduce image size.
In terms of stats, it depends upon the number of python packages
multiplied by their respective size. e.g for heavy packages with a lot
of dependencies it reduces a lot by don't cache pip packages.

Further, more detailed information can be found at

https://medium.com/sciforce/strategies-of-docker-images-optimization-2ca9cc5719b6



Signed-off-by: Pratik Raj <Rajpratik71@gmail.com>

Dockerfile

@@ -12,17 +12,17 @@ WORKDIR /app
 COPY requirements /app/requirements
 
 # py dev tooling
-RUN python3 -m pip install --upgrade pip && python3 --version
-RUN pip3 install --upgrade setuptools
-RUN pip3 install -r requirements/app.txt -r requirements/dev.txt -r requirements/test.txt
+RUN python3 -m pip install --no-cache-dir  --upgrade pip && python3 --version
+RUN pip3 install --no-cache-dir --upgrade setuptools
+RUN pip3 install --no-cache-dir -r requirements/app.txt -r requirements/dev.txt -r requirements/test.txt
 
 # Copy code and meta/config data
 COPY setup.* .flaskenv wsgi.py /app/
 COPY flexmeasures/ /app/flexmeasures
 RUN find . | grep -E "(__pycache__|\.pyc|\.pyo$)" | xargs rm -rf
 COPY .git/ /app/.git
 
-RUN pip3 install .
+RUN pip3 install --no-cache-dir .
 
 EXPOSE 5000