Develop canonical grid files / definitions

[jhamman]

We should develop a set of canonical grid files and definitions. We currently have our project grids defined in terms of a CRS and extent, e.g.

https://github.com/carbonplan/data/blob/933782082e3a788bed64ecb5541af36919acdef8/carbonplan_data/utils.py#L27-L49

These should remain the reference definitions but should be accompanied by "grid files" that include the following parameters:

• cell centroids
• cell boundaries
• land / ocean mask
• cell elevation
• cell area