allow for missing obs file w/o a JEDI crash

[rtodling]

Description

This allows for ops-class (type) to be in yaml even when input file is missing ... JEDI will warn of missing file, but it won't crash - in OPS these would need to be set more restrictively.

See documentation for specifics on options for this:
https://jointcenterforsatellitedataassimilation-jedi-docs.readthedocs-hosted.com/en/latest/inside/jedi-components/ioda/file-formats.html#missing-file-action

Dependencies

None

Impact

None

Issue

This is part of what's needed to address issue #362 - in this case, wiring the obs-classes would be ok ... but r2d2 (or swell) must be less strict and allow for job to continue when obs file is not found - this is to be done and therefore this is still a DRAFT.

[rtodling]

The knob placed here will no fully work as they should. They only work when some filters are not present. This knob is supposed to create an zero-ob observer object corresponding to the missing instrument and create allow for things like satbias and satbias_cov (for radiance) to be propagated even in the absence of the instrument - which is what we want. Unfortunately, some of the filters don't work properly in the absence of observations (zero-ops) so the quest is now one of finding the offending filters and get them fixed; a non-trivial task.

[gmao-yzhu]

The changes made are necessary. At the same time, in terms of the JEDI code workflow, when data are missing, the filters should all be skipped.

[gmao-jjin3]

I made a few minor updates based on this PR. So far, my PR #415 works for missing convectional, ozone, and microwave radiance data. It crashes swell-3dfgat_atmos run when any of AIRS, IASI, CRIS-FSR, and AVHRR input files is missing.