Review loading of filter information

[AarynnCarter]

Currently, filter information can be ported into spaceKLIP through two possible resources:

1. WebbPSF, which uses ETC engine files
2. SVO FPS, which uses... something.

The value are slightly different between each, potentially due to how the wavelengths are defined (WebbPSF uses a bp.avgwave(), whereas SVO uses the effective wavelength).

There is an issue in that SVO does not have the MIRI FND filter, so currently WebbPSF must be used for the MIRI filters. These are the lines in question from database.py:

# Load NIRCam, NIRISS, and MIRI filters
wave_nircam, weff_nircam, do_svo = get_filter_info('NIRCAM', return_more=True)
wave_niriss, weff_niriss = get_filter_info('NIRISS', do_svo=do_svo)
wave_miri,   weff_miri   = get_filter_info('MIRI',   do_svo=False) 

Ideally, we should homogenise the approach, and use the same resource for each instrument. OR ensure that WebbPSF and SVOFPS give consistent results, so that using WebbPSF for MIRI is not a significant issue.