Implement support for NIRCam DHS sub apertures

[mperrin]

Implements support for computing monochromatic PSFs for the NIRCam Dispersed Hartmann Sensor (DHS) mode. Intended for ETC PSF generation in support of implementing a TSO mode using the DHS.

Requires updated data files to work.

[pep8speaks]

Hello @mperrin, Thank you for submitting the Pull Request !

• In the file webbpsf/webbpsf_core.py:

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If you have not done so, please lint your code in accordance with best practices.

[obi-wan76]

This looks good to me, below are some of the pupil and PSF for all the DHS apertures.