Draft: Adding an app for analytical benchmarking

This extra app under the folder 2024-convbench basically solves the Stokes system for freeslip-freeslip and noslip-freeslip boundary condition cases on a thick spherical shell and calculates the L2 error with the analytical solution. It calls python routines inside the interpolate function to get the analytical solutions from the assess python package. More details on using the app is in readme.md.

Major additions would be

1. P2P1ElementwiseBlendingFullViscousStokesOperator, which basically uses the full viscous operator forms for the velocity block

   • \eta\left((\nabla u + \nabla u^\top) - \frac{2}{3}\nabla\cdot u\right)

2. PythonCallingWrapper, a simple class to call a Python function which returns a list and is returned as an std::vector

The next step would be to create a test with this.