New base layer

[BaBoWaGa]

Checklist

• [X] I've searched through the current issues to make sure this feature hasn't been requested already.

Motivation

Hello, I would like to add OpenTopoMap as a base layer I have tried several json variants but nothing. Perhaps it would also be useful to better document how to insert OpenTopoMap or other base layers. Regards

Suggested solution

It would be useful to be able to add more alternatives

Alternatives considered

No response