Migrate to .NET 8

[PavelBal]

To be used with rSharp in ospsuite R package.

• [x] Enable test-utilities-individual in ospsuite R package
• [x] Enable test-utilities-population in ospsuite R package
• [x] Move create-individual and create-run-population vignettes back from WIP folder.
• [x] Uncomment entries in pkgdown.yml

[Yuri05]

• convert ospsuite.R and below to .net8 (if .net framework 4.x)
• create additional nuget package with all dependencies required for ospsuite-R (incl. PK-Sim dlls and 'OSPSuite.Core dlls)
• use that nuget package in ospsuite-R (and remove the copies of ospsuite.core dlls from hte ospsuite-R repo)

[rwmcintosh]

Issue	Description	Status
https://github.com/Open-Systems-Pharmacology/PK-Sim/issues/2912	convert ospsuite.R and below to .net8 (if .net framework 4.x)	done
#2909	create additional nuget package with all dependencies required for ospsuite-R (incl. PK-Sim dlls and 'OSPSuite.Core DLLs)	done
https://github.com/Open-Systems-Pharmacology/OSPSuite-R/issues/1422	use that nuget package in ospsuite-R (and remove the copies of ospsuite.core dlls from hte ospsuite-R repo)	done
https://github.com/Open-Systems-Pharmacology/OSPSuite-R/issues/1432	Release workflow	not required
#2931	allow initialization of PKSim.R in Ubuntu

[rwmcintosh]

We are approaching this a little bit in reverse. We are creating the dependency resolution project first and will decouple OSPSuite-R from OSPSuite.Core (although they will be indirectly coupled through PK-Sim). That means that only PK-Sim will deliver assemblies to OSPSuite-R and there is no chance of mismatch.

With that, there will be some changes in OSPSuite-R (eg. initPKSim will need revision).

After that is all in place, we can update the dependency resolution project and everything below.

[PavelBal]

Done!