Add dust emissions

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@jfkok has done some great work pulling together dust emissions. This issue is for tracking their inclusion in input4MIPs.

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An initial draft of the files is here, which includes a nice briefing on how to use the data.

My initial comments on this are:

• the way the files are currently written, the scenario (historical, future increase, future decrease, future constant) and the region (global or regional) are both blended into the variable name. That isn’t how most of the data is handled. The more common pattern for this (where the variable is the same every time if I am not mistaken) would be to use the same variable name for every file (e.g. dustscalefactor) and then the region of application is identified by the grid label. It’s a bit weird, but the current practice is to identify the scenario by the source ID (although I think we could do something clearer than this, full discussion is here: Altering the DRS #64).
• is there a reason that future starts in 2001? That will be different to how ScenarioMIP will be handling the split buf it this is for a custom experiment, it may not matter (but it will matter if we want these dust emissions included in the DECK’s historical experiment)
• the data does present a bit of a challenge for input4MIPs (the same comments apply to Stephanie’s data and it would be great to address them for CMIP7 (in CMIP6 there unfortunately wasn’t time)). The data has this idea of regions to which the data applies. The CF conventions do have a standard for this (https://cfconventions.org/Data/cf-conventions/cf-conventions-1.11/cf-conventions.html#geographic-regions), which is probably what we would want to use. I think that would then all just work, but it might require a bit of a tweak to how the data is written(and the grid label for regional stuff would probably then become “gr”, see the full list of options here: https://github.com/PCMDI/mip-cmor-tables/blob/main/MIP_grid_label.json).
• Just to check my understanding: the variable is the same every time right? It’s a scaling factor and the idea is that models use this to scale their internally calculated dust to get closer to the change in dust over time?

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@jfkok making sure you get a notification and can find this