fix(instrumentation-runtime-node): use the correct unit for eventloop.utilization

[maryliag]

Which problem is this PR solving?

• Fix nodejs.eventloop.utilization under instrumentation-runtime-node is a percentage, not a duration #2630

Short description of the changes

• Unit of the metric eventloop.utilization was wrongly using s, instead of the unit 1, as defined its semantic convention

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.79%. Comparing base (4cfcc59) to head (320f48b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2631   +/-   ##
=======================================
  Coverage   90.79%   90.79%           
=======================================
  Files         169      169           
  Lines        8059     8059           
  Branches     1645     1645           
=======================================
  Hits         7317     7317           
  Misses        742      742           

Files with missing lines	Coverage Δ
...-node/src/metrics/eventLoopUtilizationCollector.ts	88.23% <ø> (ø)

[pichlermarc]

looks good, thank you 🙂