Update the Grids configuration

Change the way the Grids are done. Creating a new class for each possible option using python dataclasses.

For example:

from dataclasses import dataclass

@dataclass
class CAMS(Grid):
    centre_lat: float = 35.
    centre_lon: float = 20.
    west: float = -51.
    south: float = -35.
    dlon: float = 0.1
    dlat: float = 0.1
    
    ...

Instead of writing the grid config in the satillite yaml config. So then the user would only have to specify the which grid they want grid_repr="cams". Or add a new grid repr that they want.

@cgile @eemili @gmonteil