Support Mapbox alternatives to make contributing easier

[th0rgall]

It seems one needs to provide payment details to Mapbox to get an access token for testing.

We already combine Mapbox with the open MapLibre libraries, but we still use the Mapbox API token, at least for geocoding, map styles, and vector tiles. There might be more use cases too.

We could probably provide fallback open/free options for these APIs to encourage open development. The map itself is an essential part of the user experience, so it's hard to develop/fix features without being able to see the map.