Allow larger tile size limit

https://github.com/mapbox/tippecanoe/blob/18e53cd7fb9ae6be8b89d817d69d3ce06f30eb9d/tile-join.cpp#L517-L518

tile-join skips tiles that are larger than 500K. However, Mapbox now allows (and has for some time) tiles up to 2500K (and advises it may allow more in special circumstances). Please consider either raising the limit in the referenced lines of code. Or allow the use of the -M arg so users can choose to set their own limit, consistent with the tippecanoe tile generator.

Start in tile-join.cpp at lines 517-518 and trace how tile-join handles tiles over the current 500K limit. Check the existing -M behavior in the tippecanoe tile generator, then make tile-join support the requested larger or user-configurable limit; done means tiles within the selected limit are no longer skipped.

Written by the indexing model from the issue text.