Feature/mwsfy3 cx varobs

[david-rundle]

Added a namelist to create cx files for MWSFY3 with stash items 266,267,268 as for all the other instruments and unit test.

[brettcandy]

this looks complete to me. I have checked that the mwsfy3 test is correctly installed and ran ok. Good to merge

[yaswant]

@david-rundle are you okay to do a merge develop?

[DJDavies2]

I am getting this failure:

Using default value: Error: Variable ice_cloud_volume_fraction_in_atmosphere_layer not found in Data/cx_globalnamelist_mwsfy3.nc4 OOPS Ending 2023-05-15 13:36:46 (UTC+0000)

in test_opsinputs_cxwriter_globalnamelist_mwsfy3.