Add peer service to client spans

[grcevski]

This PR adds the span attribute "peer.service" as per the spec for client calls https://opentelemetry.io/docs/specs/semconv/registry/attributes/peer/.

We only set the peer if there's a host name resolved, not using IP addresses.

Fixes #800

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.09%. Comparing base (82fdcc3) to head (14a6b6e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/appolly/app/request/metric_attributes.go	75.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #854      +/-   ##
==========================================
- Coverage   55.37%   55.09%   -0.29%     
==========================================
  Files         251      251              
  Lines       21443    21459      +16     
==========================================
- Hits        11875    11822      -53     
- Misses       8757     8822      +65     
- Partials      811      815       +4     

Flag	Coverage Δ
integration-test	23.25% <0.00%> (-0.03%)	⬇️
integration-test-arm	0.00% <0.00%> (ø)
integration-test-vm-${ARCH}-${KERNEL_VERSION}	?
k8s-integration-test	2.76% <0.00%> (-0.01%)	⬇️
oats-test	0.00% <0.00%> (ø)
unittests	46.22% <87.50%> (-0.28%)	⬇️

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[mmat11]

lgtm!