add `url.template` to client spans

[MarcusDunn]

Added support for url.template (plus KTOR integration)

if https://github.com/ktorio/ktor/pull/4747 gets merged in. Fixes #13570. If it does not get merged, allows applications to set the attribute.

url.template is currently hard coded as it's not in the semantics package yet.

I imagine this is due to stability stuff. I'm unsure if this makes this PR unmergable.