feat: support julienschmidt/httprouter

[rarguelloF]

Adds support for github.com/julienschmidt/httprouter

Requires DataDog/dd-trace-go#2921

[RomainMuller]

LGTM; Ship only once it refers to a tagged release of dd-trace-go.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (main@3e4604d). Learn more about missing BASE report.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #332   +/-   ##
=======================================
  Coverage        ?   60.28%           
=======================================
  Files           ?      166           
  Lines           ?    11973           
  Branches        ?        0           
=======================================
  Hits            ?     7218           
  Misses          ?     4280           
  Partials        ?      475           

Components	Coverage Δ
Generators	76.98% <ø> (?)
Instruments	88.05% <ø> (?)
Go Driver	73.13% <ø> (?)
Toolexec Driver	70.64% <ø> (?)
Aspects	71.73% <ø> (?)
Injector	73.72% <ø> (?)
Job Server	63.45% <ø> (?)
Integration Test Suite	53.55% <100.00%> (?)
Other	60.28% <100.00%> (?)

Files with missing lines	Coverage Δ
...lienschmidt_httprouter/julienschmidt_httprouter.go	100.00% <100.00%> (ø)
_integration-tests/tests/mux/mux.go	100.00% <100.00%> (ø)