Support CDEs for config splits

[grasmash]

When a new CDE is created on ACE, config.settings.php should activate a corresponding config split. All CDEs should probably use the same split. E.g., 'ci' or 'cde'.

[grasmash]

@arknoll @geerlingguy Let me know if you think this makes sense.

[arknoll]

Yeah, this is the same sort of problem I was mentioning with Acquia Search on CDEs. I think the most logical would be to force it into the dev split. If a team wants to override it they can just adjust their settings.php below blt's config include.

[geerlingguy]

I would default to dev. Failing that, cde. It's definitely going to be different than the typical ci environment, if devs can log into sites running on them and use them like they would one of the normal cloud environments.

[grasmash]

I've created an ah_other split to handle both RA envs and CDEs. #1331