Replace hardcoded python version with ARG variable The Dockerfile had a hardcoded Python version in install paths and COPY command in the second stage build. Replace that with a hardcoded ARG pythonversion. Add RUN command to verify pythonversion against the actual version installed in the docker image. If they do not match generate an appropriate --build-arg for the docker build command that will match the docker image version. Document the use of the variable and why it's needed in installation.txt. Also fix typos referencing --build-args and bad values for the arguments.

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