FTR: metadata useful for widefield data

Channeling metadata @annechurchland (thank you!) has reported (during NWB Adoption session) to be useful for widefield data:

```
Metadata for widefield:
Mouse
Light source, wavelength, intensity at sample
Optocal system (NA, resolution)
Camera
Focusing depth
Surgery (window or clear skull prep; qc)
Imaging speed
expression/indicator/injection(I guess that is included in mouse?)
width and height pixels,
magnification (same info as resolution I guess),
objective aperture,
wavelength need to be per channel,
light shielding (essential for rolling shutter - details on the shielding method are useful for reproducibility),
shutter mode (rolling/global),
cam exposure - not necessarily the same as frame rate,
illumination exposure - can be dictated by the common time of all lines,
exposure filter bandwidth,
exposure dichroic cutoff,
excitation dichroic cutoff,
```
whenever I have mentioned BEP031 (https://github.com/bids-standard/bids-specification/pull/881)