Also allow entering WTMS Imagery URLs in addition to GetCapabilities URLs

[jidanni]

Just as https://josm.openstreetmap.de/wiki/Help/Preferences/Imagery
says, WTMS is missing.

And what's worse, one cannot add WTMS Imagery URLs!

In "Imagery Preferences" > Imagery Providers, there at the bottom left is
a +WTMS button.

It asks "Enter GetCapabilities URL"

(P.S., I have to type the above words in by hand as
I am not allowed to copy them.

I feel like my Mom, who never learned how to copy and paste.)

Alas, some sites e.g.,
​https://opentopomap.org/about
only lists a imagery URL, not a GetCapabilities URL.

And indeed some sites may not even have a GetCapabilities URL.

And in the "Selected entries:" there are only "Imagery URL"s shown, no
GetCapabilities URLs shown anyway. Nor any right click to show what they
were. The program probably probes them once and throws them away anyway...

Therefore please also allow entering imagery URLs in addition to
GetCapabilities URLs.

(Or have the program, taking the imagery, initiate a probe to all the
usual places(?) the corresponding GetCapabilities URL may be.)

Anyway, the impression is: here is the mighty JOSM, but I can't even
tell it to use ​http://{switch:a,b,c}.tile.openxyz...