
Create a GTI tile index layer from a source table.
gti_index_create.Rdentries must have a location column (paths / VSI URLs) and either
a geom column (WKT polygons in crs) or xmin/ymin/xmax/ymax
columns. All other columns become index fields (numeric -> Real,
otherwise String); a datetime column enables per-slice FILTERs and
SORT_FIELD ordering.