Add a CMIP7 version option of the CO2 data

[ekluzek]

There are new CO2 datasets for CMIP7. So we should add new "cmip7_20tr" options for it to the XML option DATM_CO2_TSERIES.

There's a host of other options for all the CMIP6 SSP's. I suggest we just add new ones for CMIP7 and leave the SSP's as they are for CMIP6 and have both CMIP6/CMIP7 options available for historical. We should also add an option "cmip6_20tr" and "cmip6_20tr.latbnd" to distinquish. And then phase out the plain "20tr" and "20tr.latbnd".

When we get the CMIP7 SSP's in we should possibly just have only the CMIP7 versions available out of the box.

@slevis-lmwg @alperaltuntas @mnlevy1981 @klindsay28

[ekluzek]

Pinging a couple others about this:

@briandobbins @fvitt

We talked about this in a couple CSEG meetings. August 5th we have this:

Erik: For CTSM/MOM we need to add CMIP7 CO2 to datm. Who in CAM has worked with the CMIP7 CO2 datasets that we can coordinate with? Who has the most time in the group that needs it – to do this? Brian will ask about this. Mike is the contact for Ocean, Erik for Land. CICE doesn’t need CO2.
CO2: Francis or the ACOM group might know about this for CAM. Brian will ask Cecile