Number of columns is always 1 by definition.

Adding support for 2dm files

See merge request ogs/ogs!4250

[PL/Output] Small refactorization / improvements

See merge request ogs/ogs!4262

Output file are directly connected to resources. These resources should be
uniquely associated to one OutputFile object. Thus, it shouldn't be possible to
copy an object of class OutputFile.

[PL/Output] Tests and fixes for `class OutputDataSpecification`

See merge request ogs/ogs!4257

[PL/TRM] Pass several variables to MPL properties

See merge request ogs/ogs!4260

The TransportPorosityFromMassBalance and PorosityFromMassBalance need
volumetric_strain, effective_pore_pressure, and porosity to be set. The
later called van-Genuchten relation also needs capillary_pressure to be
set.

TH2M Dissolution of gas components in liquid phase

See merge request ogs/ogs!4131

tests for fixed_output_times method
tests for repeat-each-steps method

also checking the diffusion and phase appearance.