Add tile size to metadata

In a future version, a tile size metadata option should be considered. Mapbox vector tiles are 512 square pixels in size, but raster tiles traditionally have been 256 square pixels, but in the last couple years, some have started moving to larger sizes. When it comes to storing the tiles in SQLite, the tile size makes no difference, but when rendering data, the tile size will often be needed. Adding an optional column to the metadata table for table size would address this. There is a similar request for the TileJSON spec here: https://github.com/mapbox/tilejson-spec/issues/26

Start by reviewing the MBTiles specification's metadata table and the related TileJSON request linked in the issue. Determine the scope and compatibility requirements for an optional tile-size metadata field; done means the specification clearly records the agreed field and its semantics.

Written by the indexing model from the issue text.