Inconsistent API in setting normalization of the power spectrum

[AlexGKim]

The script flip_compute_power_spectra.py has a normalize_power_spectrum keyword the doesn't exist and is inconsistent with normalization_power_spectrum in power_spectra.generator.py.

https://github.com/corentinravoux/flip/blob/01a9be97412d49bc9e55832b721754cb6127c4ef/scripts/flip_compute_power_spectra.py#L40C5-L40C55

[corentinravoux]

Closed with the PR #33