Add dust_emission_method to drv_flds_in

[ekluzek]

We need to add a new field to drv_flds_in that will be used by both CTSM and CAM. There is current work at adding a new dust emission scheme to CTSM. Both CTSM and CAM will need to know which scheme is being used. CTSM will toggle between the schemes and CAM needs to know which scheme is used in order to set the dust_emis_fact dust tuning factor.

Currently the only option is the Zender scheme, but Leung-2022 will be added as will a prescribed dust emissions mode.

Similar to other fields this will be able to be set by either CAM or CTSM with an error occurring if they disagree with each other. The field will then get passed down to both ATM and LND from the driver.

This was worked out in a meeting with @fvitt and others.

Definition of Done:

• [x] New FORTRAN code shr_dust_emis_mod.F90 in cesm/nuopc_cap_share
• [x] Update namelist defaults for new namelist items: dust_emission_method and zender_soil_erod_source

[ekluzek]

The group name should be: dust_emis_nl, and another variable to add to it is: zender_soil_erod_source (which can be lnd or atm, or none).

[ekluzek]

A design doc for this is here:

https://docs.google.com/document/d/18nZ3LJF5W-YF9iBhqed6s_NWeKOvSSL2-k0Lye1nnLg

[ekluzek]

Estimate for this development

1. [x] Develop FORTRAN code 24-40
2. [x] Add to drv_flds_in namelist, and test it in CMEPS 4
3. [x] Decide and/or develop tests to be added to CMEPS 1-4 (will be a unit tester in CTSM)
4. [x] Test in CTSM 4-8
5. [ ] Update to latest versions, run testing 1 -4
6. [ ] Respond to reviews and have the tag made 1-3

Min: 35 Avg: 63 Max: 75

Estimate from average of above: 58

[ekluzek]

#407 is the short follow on project to this.