Added sampling options when an inbound traceparent exists

[jbedell-newrelic]

New config options for how to sample when we have sampling data from an upstream entity.

Possible values:
default: New Relic's standard sampling rules will be used.
always_on: Always sample spans in this case.
always_off: Always skip sampling in this case.

YML config

distributed_tracing:
    sampler:
      remote_parent_sampled: default
      remote_parent_not_sampled: default

So, setting remote_parent_sampled to always_on would tell the agent to try and always sample anything that an upstream entity told us was sampled, until the sampling reservoir is full.

Or, setting remote_parent_not_sampled to always_off would tell the agent to not bother sampling anything if the upstream entity told us that it was not sampled.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 81.81818% with 4 lines in your changes missing coverage. Please review.

Project coverage is 70.55%. Comparing base (76029c1) to head (f983d50).

Files with missing lines	Patch %	Lines
.../src/main/java/com/newrelic/agent/Transaction.java	73.33%	1 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2279      +/-   ##
============================================
- Coverage     70.77%   70.55%   -0.23%     
+ Complexity    10186    10030     -156     
============================================
  Files           844      844              
  Lines         41171    40590     -581     
  Branches       6301     6155     -146     
============================================
- Hits          29139    28637     -502     
+ Misses         9224     9171      -53     
+ Partials       2808     2782      -26     

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[jbedell-newrelic]

Resolves #2222