Closes #3102.

The usage of CPMFindPackage instead of CPMAddPackage searches for
local installs of the package first and falls back to CPM if not
found.

Had to make some modifications to iphreeqc:

https://github.com/ufz/iphreeqc/commit/b1047d3eb03e7ef1b850231be35acb9c6a2cf345

Was not in use anymore.

Are already called in `ogs_add_library()`.

Submodule commit b0bc24cfdda39b30145b1f6c2c84b801cd131fef was not available anymore in the master branch of ArashPartow/exprtk.
The branch was maybe rebased? Used commit c7c219480d9678eec7383a4a99030683c4a84d91 instead (same commit date).

https://github.com/cpm-cmake/CPM.cmake

[utils] Creating voxel grid from layers

See merge request ogs/ogs!3433

Small fixes

See merge request ogs/ogs!3443

[utils] added voting mechanic to bridge small discontinuities such as horizon-shifts due to faults, adjusted test to reflect this change

add FormEigenVector MPL util

See merge request ogs/ogs!3442

Local Newton-Raphson updates

See merge request ogs/ogs!3440

RM; double porosity model

See merge request ogs/ogs!3405