Allow different projections in custom WMS menu

[tordans]

Linking other issues:

This is a follow up to my ticket #8057.

There are/were quite a few WMS issues and PRs over time (Ping #4977). But I could not find a current one to track extending the custom WMS dialogue to allow changing projections.

The latest info seems to be #6915 (comment); which was merged via #7510.

I ended up including a limited version of this in …
For now, iD can support custom wms templates but we will assume EPSG:3857 for the projection. (I didn't have time to add an input field for the user to type in some different projection or validate it against the limited list of projections iD actually supports)

---

Feature Request:

• Provide a way to choose the projection, that a custom WMS url uses, so that any WMS URL from ELI can also be used directly as custom WMS url.
• Optionally: Give some error feedback in the UI if the requests fails eg. with a 400 or 500 which would indicate a error in the URL or projection

---

Example from #8057

When I use the 2011 data from ELI (step 3 in #8057), I get this URL for a tile (which works):
https://fbinter.stadt-berlin.de/fb/wms/senstadt/k_luftbild2011_20?LAYERS=0&STYLES=default&FORMAT=image/png&SRS=EPSG:4326&WIDTH=256&HEIGHT=256&BBOX=13.408813476562502,52.50619134203458,13.411560058593746,52.50786308797267&VERSION=1.1.1&SERVICE=WMS&REQUEST=GetMap

• EPSG:4326
• BBOX=13.408813476562502,52.50619134203458,13.411560058593746,52.50786308797267

When I use the 2011 data-url as custom layer (step 4 in #8057), I get this URL (which does not work):
https://fbinter.stadt-berlin.de/fb/wms/senstadt/k_luftbild2011_20?LAYERS=0&STYLES=default&FORMAT=image/png&SRS=EPSG:3857&WIDTH=256&HEIGHT=256&BBOX=0,-7.081154550627917e-10,10018754.17,10018754.170000002&VERSION=1.1.1&SERVICE=WMS&REQUEST=GetMap

• EPSG:3857
• BBOX=0,-7.081154550627917e-10,10018754.17,10018754.170000002

Similar problem for https://isk.geobasis-bb.de/mapproxy/dgm/service/wms?FORMAT=image/jpeg&TRANSPARENT=TRUE&VERSION=1.1.1&SERVICE=WMS&REQUEST=GetMap&LAYERS=dgm&STYLES=&SRS={proj}&WIDTH={width}&HEIGHT={height}&BBOX={bbox}