Modify uwsgi entrypoint to allow for overriding settings.py

[mtesauro]

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This minor enhancement adds an if statement to the existing entrypoint_uswgi.sh to allow the settings file in a container to be overridden by one that is bind mounted or otherwise injected into the container at /settings/. If the uwsgi container is started with the path /settings/settings.py, that settings.py file will overwrite the one 'baked" into the Docker container.

Note: If you don't inject a file at /settings/settings.py via a bind mount or similar, there is no change to the current behaviour for the uwsgi container so this will not break any existing container deployments.

This was originally created to work around a bug in django-environ where the conversion of a Bash environmental variable to a complex Python Dict failed. However, it can be useful in other ways as well such as:

• allowing easy direct editing of settings.py from outside the container
• quickly editing/testing changes to settings.py
• For CI/CD, re-using the same docker-compose for multiple changes to settings.py
• that cool thing you think of :-)

This was tested with the following bind mount for the uwsgi container using docker-compose:

      - type: bind
        source: /opt/dojo/settings
        target: /settings

where

$ ls /opt/dojo/settings
settings.py