Include stack traces in client spans

[sdaubin]

Overview

This includes stack traces in client spans. The attribute key name is code.stacktrace.

The DT and transaction trace UIs will be updated to display the stack traces.

Testing

You can use the UI builds from this PR to test with an agent.

The agent includes a suite of tests which should be used to
verify your changes don't break existing functionality. These tests will run with
Github Actions when a pull request is made. More details on running the tests locally can be found
here,

Checks

[ ] Are your contributions backwards compatible with relevant frameworks and APIs?
[ ] Does your code contain any breaking changes? Please describe.
[ ] Does your code introduce any new dependencies? Please describe.

[codecov-commenter]

Codecov Report

Merging #1507 (a3819b9) into main (b50676a) will increase coverage by 70.61%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##             main    #1507       +/-   ##
===========================================
+ Coverage        0   70.61%   +70.61%     
- Complexity      0     9752     +9752     
===========================================
  Files           0      813      +813     
  Lines           0    39280    +39280     
  Branches        0     5964     +5964     
===========================================
+ Hits            0    27736    +27736     
- Misses          0     8860     +8860     
- Partials        0     2684     +2684     

Files	Coverage Δ
...elic/agent/service/analytics/SpanEventFactory.java	88.69% <100.00%> (ø)
...lic/agent/service/analytics/TracerToSpanEvent.java	98.01% <100.00%> (ø)
.../main/java/com/newrelic/agent/model/SpanEvent.java	81.33% <0.00%> (ø)

... and 810 files with indirect coverage changes

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[jasonjkeller]

This PR has been replaced by PR #1520