User configurable tile styles / url templates

[vorbei]

in https://github.com/neocarto/bertin/blob/main/src/layers/tiles.js
the 'style' parameter only supports string type, and not user extendable.

for a custom style/url, please consider support Object parameter like

{
     name: "openstreetmap",
     provider: "OpenStreetMap contributors",
     url: (x, y, z) => `https://tile.openstreetmap.org/${z}/${x}/${y}.png`,
   },

[neocarto]

Thank you for this PR. It is available in bertin@1.0.6.
I have removed the "name" property which is useless in this case.
See section 4 of this notebook: https://observablehq.com/@neocartocnrs/bertin-js-tiles?collection=@neocartocnrs/bertin
Thanks again :-)