Nbp with product pool fluxes.

[rosiealice]

Description of changes

Updated co2 flux when fates is on.

Includes nbp calculations:
NBP=NPP-fire_closs-grazing_closs-product_loss
Net carbon exchange is positive to atm.

Specific notes

Contributors other than yourself, if any:

CTSM Issues Fixed (include github issue #):

Are answers expected to change (and if so in what way)?

Any User Interface Changes (namelist or namelist defaults changes)?

Does this create a need to change or add documentation? Did you do so?

Testing performed, if any:
All aux_clm_noresm tests pass.

(Documentation on system testing is here: https://github.com/ESCOMP/ctsm/wiki/System-Testing-Guide)
(aux_clm on derecho for intel/gnu and izumi for intel/gnu/nag/nvhpc is the standard for tags on master)

NOTE: Be sure to check your coding style against the standard
(https://github.com/ESCOMP/ctsm/wiki/CTSM-coding-guidelines) and review
the list of common problems to watch out for
(https://github.com/ESCOMP/CTSM/wiki/List-of-common-problems).

[rosiealice]

@maritsandstad @kjetilaas I think this PR is ready to be merged, but as I am feeling both a little dizzy and kindof on shaky ground with this tagging business, I wondered if one of you could take a look at it? I'm up to the point where it needs merging (see the notes I made in the discussion for the other PR here) following which the final stage is to make a push a ctsm tag and then the new noresm tag.

The other thing, as I noted, is that the product pool variable here is in the soilbgc rather than the fates interface - I had forgotten in my delirium that Matvey suggested i should do that. But in order to avoid getting any sicker I am cutting my losses here and tidying it up will need to be TBD (sorry!)

[maritsandstad]

Happy to look at this later today/this afternoon. Just relax and get better @rosiealice

[maritsandstad]

Can't push to your branch, and probably can't merge in there either so I am fixing the rest of this here: #148