[cmake] Enable Python bindings for TFEL

Python bindings for TFEL are enabled if OGS_USE_PYTHON=ON and the dependency libboost_python[py version] is available. On our envinf machines you have to specify to use Python 3.10 as the boost package is compiled with it.

On TFEL building (during first CMake run) instructions on PYTHONPATH setup are printed, e.g.:

-- TFEL build with Python bindings. To use them:
   export PYTHONPATH=/home/bilke/code/ogs/build/release/_ext/TFEL/lib/python3.10/site-packages:$PYTHONPATH

Then you can use it in Python, full example (valid on envinf[x]) e.g.:

➜ cd ogs
➜ rm -r ../build/release-all
➜ cmake --preset release-all -DPython_EXECUTABLE=/usr/bin/python3.10
➜ export PYTHONPATH=/home/bilke/code/ogs/build/release/_ext/TFEL/lib/python3.10/site-packages:$PYTHONPATH
➜ python3.10              
Python 3.10.8 (main, Nov  1 2022, 14:18:21) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import mtest
>>>

cc: @FZill, @felikskiszkurno

1. Feature description was added to the changelog