Transfer metadata across GDAL metadata XML and geometamaker YML

[davemfish]

If a GDAL dataset already has some user-defined metadata, it would be nice preserve that and include it in the Resource. Similarly, if a user sets attributes of a Resource, it might be nice to also set the corresponding GDAL metadata attributes. The idea is that some people may routinely interact with metadata using GDAL, or other GIS software, and we would like geometamaker metadata to stay in sync.

[davemfish]

Also, for rasters, we could consider including statistics in the Resource when they are available (e.g. GetStatistics). So far we have avoided calculating stats in geometamaker because of the costs involved for doing so with remote datasets or very large datasets. But if stats are already calculated, it would be nice to include them in our metadata.