Add SMAP L3 soil moisture

[RitwikGupta]

No description provided.

[RitwikGupta]

The SMAP data is large (675M for the H5 file). This may make tests fail due to a timeout on GitHub Actions. Any ideas @cjrd?

[cjrd]

For the test, I think it's fine to just download and inspect the metadata asset. At least it's pulling something from the servers, so it'll still be a smoke test on the collection.

[RitwikGupta]

@cjrd but then the notebook is not able to show a proper plot, or at least the integration test will fail on the plotting step. So far the tests are running okay without failure.

[cjrd]

how about wrapping the big data download and plotting in a

if False:
   # change to True to download 600mb+ data and plot results

I don't think we want the tests to download that much data (even if they pass). This way ^^^ we can download the metadata and check it and have a nice plotting functionality for anyone looking to experiment with this data.