Update CLMBuildNamelist to allow AD spinup with FATES (not SP)

[adrifoster]

Description of changes

Updated CLMBuildNamelist to allow AD spinup with FATES (anything other than FATES-SP) turned on.

Specific notes

• added some helper variables to check viability of spinup
• added check to only turn on reseed_dead_plants if spinup AND CN

Contributors other than yourself, if any:

CTSM Issues Fixed (include github issue #): resolves #3771

Are answers expected to change (and if so in what way)? No because we weren't able to run AD mode before?

Any User Interface Changes (namelist or namelist defaults changes)? No

Does this create a need to change or add documentation? Did you do so? No

Will need to test the buildnamelist but everything else should be b4b

@ekluzek I did my best but please feel free to suggest updates given your pearl expertise

[ekluzek]

The logic here looks right to me. And I think it's clear and easy to see what it's doing and it takes care of both fates and BGC type cases. So thumbs up there.

We do need to add some tests around this though to the namelist tester. There are a bunch of spinup tests there, but we should add some for FATES. And we need to make sure the current ones still work.

As something to work on after this PR, for usability we will want the FATES spinup sequence to be encapsulated into the CLM_ACCELERATED_SPINIP option. Or possibly in a different option. Could you lead me through how that works and we can think about how this should work?

[adrifoster]

The logic here looks right to me. And I think it's clear and easy to see what it's doing and it takes care of both fates and BGC type cases. So thumbs up there.

We do need to add some tests around this though to the namelist tester. There are a bunch of spinup tests there, but we should add some for FATES. And we need to make sure the current ones still work.

As something to work on after this PR, for usability we will want the FATES spinup sequence to be encapsulated into the CLM_ACCELERATED_SPINIP option. Or possibly in a different option. Could you lead me through how that works and we can think about how this should work?

Thanks for this review Erik. Just to clarify, are you asking for some bldnamelist tests for this PR?