This reverts commit 707e3aa0.

Replace boost::optional with std::optional

See merge request ogs/ogs!3502

[T/RM] Update reference. RHS includes stresses.

See merge request ogs/ogs!3503

In 6fceafae "[PL/RM] Use initial stress in assemble()."
the rhs vector was changed, now including also stress
related parts, and not only the gravitational forces.

This changes only the NodalForces output, everything else
is exactly same as before.

Optional references are not allowed by std.
Replacing with semantically equivalent pointer.

boost::none -> std::nullopt
boost::make_optional -> std::make_optional
boost::optional<T>::get() -> std::optional<T>::value()

[cpm] Boost header only and skip formatting targets

See merge request ogs/ogs!3501

[CMake] Added clean_coverage target.

See merge request ogs/ogs!3499

[cpm] Fixed shapelib used from system

See merge request ogs/ogs!3500

[T/RM] Relax tolerances for failing CI job.

See merge request ogs/ogs!3497

win

Clang and CMake Format preparation

See merge request ogs/ogs!3496

[T/RM] Relax tolerances for failing CI job.

See merge request ogs/ogs!3495

frontend

RM fixes and cleanups

See merge request ogs/ogs!3477

From the equations we have
eps = eps_{m} + eps_{sw},
with eps_{sw} = -C_el^{-1} sigma_{sw}.

All other places are using correct sign.

solid_grain_pressure used in some density models was
not set and caused an access error in the ExponentialProperty.

Using central differences for Jacobian computation.
Still the HydraulicFlow and Nodal forces are not correct
and don't include the 'M \dot{x} + K x' part.

Only happened in the assemble function, which does not
have a ctest with swelling.

More Conan packages moved to CPM (2nd try)

See merge request ogs/ogs!3494