Validate Database should validate standalone XML, not embedded metadata

[ethoms-usgs]

The Validate Database tool currently exports embedded metadata from the GeologicMap feature dataset and validates it through mp.exe. But NGDMB submissions require a standalone XML and the Build Metadata tool creates a record that describes all tables in the gdb, not only those in GeologicMap. Also, metadata cannot be embedded in other formats, such as the geopackage, which we may see more of in the future.

Change the Validata Database tool so that

1. It is a choice whether metadata are checked or not
2. the user picks a standalone XML file for validation
3. the tool sends the file to the USGS metadata validation service API, not mp