Adding in flag for calculating the heat flux per unit area or for total surface

[ChrisPsenica]

Heat flux is normally calculated per unit area. The "scheme" flag will allow the user to change this. The two options are "byUnitArea" which is how DAFoam normally calculates the heat flux or "total" (the new method) which returns the entire heat transfer value over the surface of interest. If "scheme" is not specified then the default value will be "byUnitArea".

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 6 lines in your changes missing coverage. Please review.

Project coverage is 86.20%. Comparing base (bd386fd) to head (1649d8f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/adjoint/DAObjFunc/DAObjFuncWallHeatFlux.C	66.66%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #704      +/-   ##
==========================================
- Coverage   86.22%   86.20%   -0.03%     
==========================================
  Files         333      333              
  Lines       22718    22727       +9     
==========================================
+ Hits        19588    19591       +3     
- Misses       3130     3136       +6     

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