Updates to account for the no tracestate use case

[jbedell-newrelic]

Customer was seeing no effect of the remote_parent configs because the tracestate header did not exist. Adjusted the code path accordingly.

Resolves: #2291

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 76.47059% with 4 lines in your changes missing coverage. Please review.

Project coverage is 70.52%. Comparing base (9be91b8) to head (af94674).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
.../src/main/java/com/newrelic/agent/Transaction.java	71.42%	0 Missing and 4 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2302      +/-   ##
============================================
- Coverage     70.68%   70.52%   -0.17%     
+ Complexity    10355    10031     -324     
============================================
  Files           844      844              
  Lines         41310    40619     -691     
  Branches       6331     6158     -173     
============================================
- Hits          29200    28645     -555     
+ Misses         9283     9187      -96     
+ Partials       2827     2787      -40     

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