ci: Add testing for the integration of geosPythonPackages in GEOS (#141)

* Improve cmake build and testing of make geosx_python_tools

* Change strategy to use already used geos Docker image

* Try pointing to specific tag version of container

* Allows the test-geos-integration to be optional when no package used in GEOS is modified

* Add readme to explain CI logic

Author: alexbenedicto