Suppress segments in HttpUrlConnection

[kanderson250]

Resolves #2337

Our HttpUrlConnection instrumentation creates a tracer for each response handler called by the HttpUrlConnection instance. We do this to ensure we have some tracer available to report the external call. This isn't ideal, because only the first tracer gets used to report the external, but it is not known at the time each tracer is created (via @Trace annotation) whether it is the first one. The result is that HttpUrlConnection transaction traces/DTs may be cluttered with a great number of response handler segments (such as getInputStream) that weren't chosen to become externals.

This PR introduces a low-verbose mode to give users the option of suppressing these non-external segments in transaction traces and DTs. This can be enabled by setting:

NEW_RELIC_CLASS_TRANSFORMER_COM_NEWRELIC_INSTRUMENTATION_HTTURLCONNECTION_VERBOSE=false, sys prop -Dnewrelic.config.class_transformer.com.newrelic.instrumentation.httpurlconnection.verbose=false, or equivalent stanza in newrelic.yml. Default setting is true (ie, non-external getInputStream and other response handler methods will be reported as before).

Implementation comments

This functionality is implemented via an internal-only API method, excludeLeaf, which has the ability to toggle the excludes tracer flag on leaf tracers, just like the annotation @Trace(excludeFromTransactionTrace=true). The difference is that the new excludeLeaf method can be called after the tracer has already been created, whereas the annotation applies only when the tracer is constructed.

excludeLeaf is a no-op everywhere but in DefaultTracer. It is also a no-op in root tracer implementations to stay consistent with our existing agent behavior that prohibits root tracers from being excluded.

We chose to make excludeLeaf (rather than a general excludeTracer) to ensure we don't unintentionally exclude parent tracers and orphan their children. However, this could be revisited in the future as a potential enhancement.

Tests

There are a few new unit tests, plus a small AIT update for the HttpUrlConnection instrumentation. AIT branch is here and test run for that against this PR is here.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 70.52%. Comparing base (a0d08e3) to head (8fcb263).
Report is 58 commits behind head on main.

Files with missing lines	Patch %	Lines
...ava/com/newrelic/agent/tracers/AbstractTracer.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2365      +/-   ##
============================================
- Coverage     70.58%   70.52%   -0.06%     
+ Complexity    10042    10034       -8     
============================================
  Files           844      844              
  Lines         40750    40635     -115     
  Branches       6191     6161      -30     
============================================
- Hits          28762    28658     -104     
+ Misses         9210     9192      -18     
- Partials       2778     2785       +7     

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