What this MR does / why does DuMux need it:
- Adds Navier-Stokes momentum model
- Hybrid parallel implementation (MPI + Threads)
- Some infrastructure for coupling with a pressure discretization is in place but this will be a different MR
- Updates the helpers for the Navier-Stokes tests to work with the diamond scheme
Notes for reviewer:
- Builds on the implementation in !2979 + cleanup + parallel implementation + tests with reference solution