Expire span metrics and service graph metrics in the OTEL exporter

[mariomac]

The traces_target_info case is a bit more complex case and will be expired in another PR, just to keep this PR small.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 91.72932% with 11 lines in your changes missing coverage. Please review.

Project coverage is 81.86%. Comparing base (09c206f) to head (faad757).
Report is 1 commits behind head on main.

Files	Patch %	Lines
pkg/export/otel/metrics.go	93.54%	4 Missing ⚠️
pkg/internal/request/span_getters.go	84.61%	2 Missing and 2 partials ⚠️
pkg/internal/request/span.go	92.85%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1062      +/-   ##
==========================================
+ Coverage   79.09%   81.86%   +2.76%     
==========================================
  Files         139      139              
  Lines       11289    11320      +31     
==========================================
+ Hits         8929     9267     +338     
+ Misses       1818     1534     -284     
+ Partials      542      519      -23     

Flag	Coverage Δ
integration-test	56.85% <53.38%> (?)
k8s-integration-test	59.07% <75.93%> (+0.08%)	⬆️
oats-test	36.94% <16.54%> (-0.11%)	⬇️
unittests	51.92% <27.06%> (-0.16%)	⬇️

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[rafaelroquetto]

LGTM - just a few side-comments/ideas. I will leave it for the experts to approve :)

[grcevski]

LGTM! Amazing, thanks!