tracker: add attestation counter metric

[DiogoSantoss]

Add two new metrics core_tracker_attestation_expect_total and core_tracker_attestation_success_total which track the count of individual attestations instead of attestation duties.

category: feature
ticket: #4102

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 70.58824% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.88%. Comparing base (c446fc0) to head (bf7f522).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
core/tracker/tracker.go	70.58%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4248      +/-   ##
==========================================
- Coverage   56.99%   56.88%   -0.12%     
==========================================
  Files         237      237              
  Lines       30857    30935      +78     
==========================================
+ Hits        17587    17596       +9     
- Misses      11034    11102      +68     
- Partials     2236     2237       +1     

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