Create function to insert baseline tiles

Create the function insert_baseline_tiles(), the first step in the EntityInitializer process. This function goes uses a boundary geometry to select all the geometrical features in a region within a source table, such as ghsl_characteristics, iterate over those geometries, and create all the Quadkey tiles at a chosen zoom level which intersect the geometry. The function then creates an entity id, and calculates the built area for every baseline features from the GHSL Characteristics table and inserts them into the exposure database entity table.