Use tile dimensions that are defined by the TMS & deprecate or remove `tile_size` config option

[robyngit]

The workflow allows configuration of custom tile sizes, but problematically, the tile dimensions (height and width) are inherently part of each Tile Matrix Set (TMS) definition. We should therefore remove or deprecate the current tile_size option in viz-staging and instead retrieve the height and width values directly from the TMS using the Morecantile library. This issue is in the viz-workflow repo because tile_size is used in both viz-staging and viz-raster.

In the future, if we need custom tile sizes, we should instead define a custom TMS. We could consider keeping tile_size as a private option for developers, since running the workflow with smaller tiles is useful for fast testing & debugging.