feat: Fix Thermal Stress Updates

[npillardou]

This PR tries to correct the thermal stress calculations based on the difference from initialTemperature in the formula.
This way, thermal stress is ONLY introduced by a temperature change from the initial stage.

[paveltomin]

Few relatively small comments:

• probably no need to introduce smallStrainUpdateThermoPoromechanics and make it different from smallStrainUpdatePoromechanics, only one updated version should be enough to avoid confusion and potential inconsistencies
• same for computeTotalStressWithInitialTemperature vs computeTotalStress

the rest seems fine to me, thanks for the efforts.

Between initialTemperature or referenceTemperature i prefer the second one, but that would require introducing it for coupled solid and making some logic around that, probably can be done later.