Explicitly support CMIP6 Decadal Prediction (DCPP) output in climpred

@haibo, it’s more likely that I spend time working on Ocean Carbon Uptake and Productivity in the CMIP6 Ensemble this week since there’s a lot of folks to collaborate with at NCAR. However, @andersy005 worked on getting DCPP supported in intake-esm, so it currently can be loaded in but there’s still some work to do.

This topic is something I’ll be thinking about over the coming months still, and we could use your help on climpred. Send me a message on the slack (Riley Brady) to let me know what you’re thinking. It would be good to chat regardless and see if there’s something we can do during the hackathon.