draft: add tracing support

[miyunari]

Summary

Release Note

Documentation

Ref:

• Extend Observability instrumentation by supporting E2E tracking cosign#4101
• provide common otel sdk initalization sigstore#2063

[codecov]

Codecov Report

❌ Patch coverage is 0% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 26.22%. Comparing base (6fd19b0) to head (739671d).
⚠️ Report is 666 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/timestamp-server/app/serve.go	0.00%	14 Missing ⚠️
cmd/timestamp-server/app/root.go	0.00%	4 Missing ⚠️
...kg/generated/restapi/configure_timestamp_server.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1398       +/-   ##
===========================================
- Coverage   52.85%   26.22%   -26.63%     
===========================================
  Files          20       55       +35     
  Lines        1209     3153     +1944     
===========================================
+ Hits          639      827      +188     
- Misses        509     2273     +1764     
+ Partials       61       53        -8     

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