Write new docs page about PSF normalizations

[mperrin]

To answer the questions which comes to the help desk about this

[obi-wan76]

I'll use this issue to update and add new examples into the WebbPSF readthedocs. This will follow comments and bugs found during the WebbPSF workshop 2022 at the end of JWST First Science Results conference. In particular:

1. Remove rebin option in various examples when calling calc_psf
2. Remove calls to pupilopd that use the old format (wave cubes), e.g., https://webbpsf.readthedocs.io/en/latest/more_examples.html#make-plots-of-encircled-energy-in-psfs-at-various-wavelengths
3. Add some examples/documents for NIRSpec, e.g., monochromatic calculation in the wavelength range, similar to the existing example for MIRI.
4. Overall update of examples on how to use WebbPSF for specific flight observations, e.g., PSF subtraction, etc.

[BradleySappington]

Heads up that should be included with this:
In the documentation examples located here

miri.image_mask = 'LRS slit'
miri.pupil_mask = 'P750L'
psf = miri.calc_psf(monochromatic=6.0e-6, display=True)

Error saying “Distortion is not implemented yet for MIRI LRS mode.”

[BradleySappington]

#684