contrib/julienschmidt/httprouter: add http.route tag to span

[asdftamir]

What does this PR do?

Add the http.route tag to the span

Motivation

Describe how to test/QA your changes

Reviewer's Checklist

• If known, an appropriate milestone has been selected; otherwise the Triage milestone is set.
• Changed code has unit tests for its functionality.
• If this interacts with the agent in a new way, a system test has been added.

[pr-commenter]

Benchmarks

Comparing candidate commit 34d0bf5 in PR branch tamir.hyman/add-http-route-to-julienschmidt with baseline commit 8c3e650 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 18 metrics, 0 unstable metrics.

[zarirhamza]

LGTM. Good call on adding tests that aren't necessarily part of http.route but are necessary to maintain consistency across testcases