Include opencv in Dockerfile RUN command

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Include python-opencv in Dockerfile RUN apt-get install command.
Remove this from requirements.txt

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The requirements.txt file has changed opencv package. Now its opencv-python-headless. Would that work? Should we still have the RUN apt-get python-opencv in dockerfile? @sandeep-ps

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Need to test if this is required in cyber2a:0.0.6 in deployed instance.