collab: Attach `User-Agent` to `handle connection` span (#35282)
This PR makes it so we attach the value from the `User-Agent` header to
the `handle connection` span.
We'll start sending this header in
https://github.com/zed-industries/zed/pull/35280.
Release Notes:
- N/A
77dc65d826Marshall Bowers committed on 7/29/2025, 5:06:27 PM· committed by GitHubparentf9224b1