Allow for .nwb standard/file format to be used for "micr"

See https://pynwb.readthedocs.io/en/stable/tutorials/domain/ophys.html for support
of various microscopy modalities within NWB.  As NWB is already supported for
other modalities, there is some support for microscopy in NWB in various tools,
and as there are datasets with .nwb -- it makes sense to allow for .nwb to be used
for microscopy data as well where appropriate.

src/schema/rules/files/raw/micr.yaml

@@ -25,6 +25,7 @@ microscopy:
     - .png
     - .tif
     - .json
+    - .nwb
   datatypes:
     - micr
   entities: