Add Support for Generating Beam alms from GRASP Files

[paganol]

We should add a function to generate beam alms directly from GRASP files, similar to how we currently handle elliptical Gaussian beams here

litebird_sim/litebird_sim/beam_synthesis.py

Lines 203 to 208 in d02e4b5

	def generate_gauss_beam_alms(
	observation: Observation,
	lmax: int,
	mmax: Optional[int] = None,
	store_in_observation: Optional[bool] = False,
	):

and here

litebird_sim/litebird_sim/simulations.py

Lines 1598 to 1603 in d02e4b5

	def get_gauss_beam_alms(
	self,
	lmax: int,
	mmax: Optional[int] = None,
	store_in_observation: Optional[bool] = False,
	):

To implement this, we’ll need to introduce a dependency on grasp2alm.

[ziotom78]

PR #447 will implement this.