Add support for HarmonicThermo thermo treatment in TBLite's frequency calculation

[Andrew-S-Rosen]

What new feature would you like to see?

TBLite works for both molecules and solids. However, right now, the freq_job in TBLite will always compute the thermochemistry under the ideal gas approximation (IdealGasThermo). This is not always applicable, so we should add support for the HarmonicThermo method as well, which is already in quacc.

We should mimic what was already done with VASP's freq_job function here. We add a thermo_method keyword argument to freq_job that takes "ideal_gas" or "harmonic", defaulting to