Allow loading layers from a WMTS layer

[nimdanitro]

I want to load layers from a WMS/WMTS server on the map and display them over the current map.
There are two main protocols / approaches to serve those layers:

• Web Map Tile Service (WMTS)
• Web Map Service (WMS)?

Problems to solve:

• define a predefined list of WMS/WMTS servers (or should this be configuration for each instance?)
• support only public layers in a first step (WMTS can also be protected by username / password).
• Add a WMTS server selection box, on click on the specific WMTS server, load the available layers with the GetCapabilities call and display them for selection.
• Add specific WTMS layer with a proper styling
• allow selections to be hidden and removed in the layer selection box => group layers by WMTS server?

This is a loose collection of WMTS Servers:

• http://wms.geo.admin.ch
• https://wmts.geo.admin.ch Documentation here https://api3.geo.admin.ch/services/sdiservices.html#wmts
• https://geo.ur.ch/wms
• https://sitn.ne.ch/ Documentation here https://sitn.ne.ch/services/docs/api/WMS/
• https://geodienste.ch/