Implement `FoamPostprocessor` system

[mattfalcone1997]

Description

Implement methods to create a system return single values from OpenFOAM results similar to the Postprocessor system in MOOSE. The single values are computed by OpenFOAM before being stored in the Postprocessor object.

Context

This will allow simple multiscale coupling with STH codes, which require single values as the input.

Outputs

Potential examples could be

• FoamSideAveragePostprocessor
• FoamSideIntegralPostprocessor

Example input file syntax

[FoamPostprocessors]
  [T_avg]
    type = FoamSideAverage
    scalars = 'T'
  []
  [m_dot]
    type=FoamSideAdvectedFluxIntegral
    scalar = 'rho'
    advected_variable='U'
  []
[]