Started work on NHGFStacData class

Added a new data class called NHGFStacData for processing data from a STAC catalog as input gridded data. @rmcd, had to omit the test that I wrote for this class because the test kept failing in the git runner test. My hunch is that this is failing because of network issues: I cannot read data from the STAC while on the DOI network. But this error could also be a intake/Stac/Zarr issue. Pushing to Dev for you to take a look at. We don't need to merge this in with the testing in its current form.