Add PAMDataset XML to _meta metadata key so that GDAL can read SilviMetric's TileDB output

[kylemann16]

GDAL TileDB driver uses PAMDataset XML as metadata to determine raster info. GDAL gets an inaccurate picture of what SilviMetrics makes otherwise.

[kylemann16]

waiting on gdal changes to get this across the line since gdal has some naming convention issues
OSGeo/gdal#13787