Catch cases where DATM_CO2_TSERIES = none but CCSM_BGC=CO2A or CO2C

**Summary:** CESM uses `CCSM_BGC` to control which components are expecting to send / receive CO2, but datm triggers a `flds_co2` flag based on `DATM_CO2_TSERIES`. Despite that setting, it seems like datm still advertises the co2 fields when `CCSM_BGC=CO2A` and `DATM_CO2_TSERIES=none`, but in that case I get errors if I try to receive them in the ocean.

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**Long Version**

Over in the MARBL driver for MOM, I'm working on adding an option to allow MOM6 to get CO2 concentration from the coupler. In a test run, starting with a CMOM compset, I set `CCSM_BGC=CO2A` but left `DATM_CO2_TSERIES=none`. Since `DATM_CO2_TSERIES=none`, datm sets `flds_co2` to False:

https://github.com/ESCOMP/CDEPS/blob/296dfaad895623cae6ef3abcd9796ac9bfa152f2/datm/cime_config/namelist_definition_datm.xml#L295-L306

And I would think that is enough to avoid advertising `Sa_co2prog` and `Sa_co2diag`:

https://github.com/ESCOMP/CDEPS/blob/69e550218bb722372162965d2ab3d26ea2a6e3d6/datm/datm_datamode_core2_mod.F90#L136-L139

However, these lines from `med.log`started showing up when I set `CCSM_BGC` to `CO2A` (leaving `DATM_CO2_TSERIES=none`):

```
(Advertise Fields):Fr_atm: Sa_co2prog
(Advertise Fields):Fr_atm: Sa_co2diag
(Advertise Fields):To_lnd: Sa_co2prog
(Advertise Fields):To_lnd: Sa_co2diag
(Advertise Fields):To_ocn: Sa_co2prog
(Advertise Fields):To_ocn: Sa_co2diag
```

And it's unclear where they are coming from. Also, the model crashes if I try to actually access those fields:

```
20230413 122708.723 ERROR PET0000 ESMF_GeomBase.F90:923 ? Object being used before creation - Bad Object
20230413 122708.723 ERROR PET0000 ESMF_FieldGet.F90:447 ESMF_FieldGetDefault Object being used before creation - Internal subroutine call returned Error
20230413 122708.723 ERROR PET0000 MED-TO-OCN:src/addon/NUOPC/src/NUOPC_Connector.F90:3007 Object being used before creation - Passing error in return code
20230413 122708.723 ERROR PET0000 ESM0001:src/addon/NUOPC/src/NUOPC_Driver.F90:2882 Object being used before creation - Phase 'IPDv05p4' Initialize for connectorComp 1 -> 4: MED-TO-OCN did not return ESMF_SUCCESS
20230413 122708.723 ERROR PET0000 ESM0001:src/addon/NUOPC/src/NUOPC_Driver.F90:1924 Object being used before creation - Passing error in return code
20230413 122708.723 ERROR PET0000 ensemble:src/addon/NUOPC/src/NUOPC_Driver.F90:2725 Object being used before creation - Phase 'IPDv02p3' Initialize for modelComp 1: ESM0001 did not return ESMF_SUCCESS
20230413 122708.723 ERROR PET0000 ensemble:src/addon/NUOPC/src/NUOPC_Driver.F90:1895 Object being used before creation - Passing error in return code
20230413 122708.723 ERROR PET0000 ensemble:src/addon/NUOPC/src/NUOPC_Driver.F90:481 Object being used before creation - Passing error in return code
20230413 122708.723 ERROR PET0000 esmApp.F90:134 Object being used before creation - Passing error in return code
20230413 122708.723 INFO PET0000 Finalizing ESMF
```

I can think of several possible solutions:

1. Change the default for `flds_co2` to be based on `CCSM_BGC` instead of `DATM_CO2_TSERIES`, and then throw an error if `flds_co2` is true but `DATM_CO2_TSERIES` is none
1. Change the default for `flds_co2` to be `(DATM_CO2_TSERIES != none) && (CCSM_BGC != none)`, and also fix whatever bug is causing CESM to advertise `Sa_co2prog` even if `flds_co2` is false
1. throw an error if `DATM_CO2_TSERIES` is none but `CCSM_BGC` is not

and I'm not terribly familiar with this code, so maybe somebody from the land side should chime in? I wouldn't be surprised if @ekluzek pointed out something in the above options that may cause problems for CTSM, and if he has an alternate solution I'd be all for it.