feat: Add reference thermal conductivity

[dkachuma]

Adds a reference thermal conductivity. The point of this is that the user might want this to be read from the vtk file for example. So we separate this from the effective thermal conductivity which is the calculated output from the thermal conductivity model.

#3956

[codecov]

Codecov Report

❌ Patch coverage is 63.15789% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.75%. Comparing base (2acb3ef) to head (7e6ed1e).
⚠️ Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
...malConductivity/SinglePhaseThermalConductivity.cpp	84.00%	4 Missing ⚠️
...ers/surfaceGeneration/EmbeddedSurfaceGenerator.cpp	0.00%	4 Missing ⚠️
...sicsSolvers/surfaceGeneration/SurfaceGenerator.cpp	0.00%	4 Missing ⚠️
...onductivity/SinglePhaseThermalConductivityBase.cpp	50.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3959      +/-   ##
===========================================
- Coverage    58.87%   58.75%   -0.13%     
===========================================
  Files         1353     1352       -1     
  Lines       112953   112868      -85     
===========================================
- Hits         66504    66312     -192     
- Misses       46449    46556     +107     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[OmarDuran]

@dkachuma thank you for your contribution. The modifications in the SurfaceGenerators look good.