add Settings data to the output files

[hirata10]

It would be good for PyIMCOM Settings to be saved in the output coadd files (maybe in the config HDU) so they are accessible to other readers without going back to PyIMCOM.

[Michael-Gabe]

I want to do this one too

[Michael-Gabe]

@hirata10 What did you have in mind to be saved into CONFIG? To my understanding, the user inputs (block, outsize, etc.) are already saved in that HDU.

[hirata10]

We were thinking of the values in pyimcom.config.Settings (so pixscale_native, sca_nside, etc.). This way this information is preserved if we ever have a version where we change these values (e.g., do an IMCOM run for JWST).