Added Hertz contact test

ProcessLib/SmallDeformation/Tests.cmake

...ta/Mechanics/Linear/PythonHertzContact/gen-unit-circle.py

...ata/Mechanics/Linear/PythonHertzContact/hertz_contact.prj

...a/Mechanics/Linear/PythonHertzContact/hertz_contact_bc.py

Tests/Data/Mechanics/Linear/PythonHertzContact/post.py

...ics/Linear/PythonHertzContact/ref_hertz_contact_ts_10.vtu

...nics/Linear/PythonHertzContact/ref_hertz_contact_ts_5.vtu

.../Data/Mechanics/Linear/PythonHertzContact/unit-circle.gml

.../Data/Mechanics/Linear/PythonHertzContact/unit-circle.vtu

...docs/benchmarks/python-bc/hertz-contact/contact_radii.png

.../docs/benchmarks/python-bc/hertz-contact/hertz-contact.md

...docs/benchmarks/python-bc/hertz-contact/hertz-contact.png

...docs/benchmarks/python-bc/hertz-contact/hertz-contact.svg

.../benchmarks/python-bc/hertz-contact/stress_at_contact.png

...t/docs/benchmarks/python-bc/hertz-contact/total_force.png