Remove default value from peer.service tag

[marcotc]

Today, the default value of the span tag peer.service does not provide the correct semantics to populated the new Inferred Service dependency experience.

The peer.service tag should only be used as an explicit user override, which is supported today by APM Ruby.

This PR removes the default value of peer.service, while keeping any explicitly values set by configuration (e.g. c.tracing.instrument :pg, peer_service: 'mydb').

If you need to keep the default values of peer.service, you can set the environment variable DD_TRACE_PEER_SERVICE_DEFAULTS_ENABLED=true to restore the behavior to before this change.

Change log entry
Yes. Remove peer services by default, to ensure compatibility with Inferred services, allowing for automatic discovery of instrumented dependencies such as databases, queues, or third-party APIs.
If you need the previous peer service behavior back, set the environment variable DD_TRACE_PEER_SERVICE_DEFAULTS_ENABLED=true.

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-02-14 23:20:53

Comparing candidate commit 6519bea in PR branch DD_TRACE_PEER_SERVICE_DEFAULTS_ENABLED with baseline commit 92e97fa in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 31 metrics, 2 unstable metrics.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.70%. Comparing base (92e97fa) to head (6519bea).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3846   +/-   ##
=======================================
  Coverage   97.70%   97.70%           
=======================================
  Files        1355     1355           
  Lines       83051    83100   +49     
  Branches     4218     4219    +1     
=======================================
+ Hits        81144    81194   +50     
+ Misses       1907     1906    -1     

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[ivoanjo]

Hey folks, is this still a thing we want to push forward?

[tatsuo48]

Hi. I'm using Inferred Service dependency experience in Ruby
So I hope to merge&release this PR.
Thank you!

[datadog-datadog-prod-us1]

Datadog Report

Branch report: DD_TRACE_PEER_SERVICE_DEFAULTS_ENABLED
Commit report: 6519bea
Test service: dd-trace-rb

✅ 0 Failed, 20591 Passed, 1371 Skipped, 3m 12.92s Total Time