Remove usage of deprecated jackson property

[manofthepeace]

Description of changes:
PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES is deprecated since Jackson 2.7 (2.12 is used). This was done to help potentially unblock quarkusio/quarkus#37295

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (398ec05) 28.08% compared to head (c9a103b) 24.27%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #391      +/-   ##
============================================
- Coverage     28.08%   24.27%   -3.81%     
+ Complexity      574      498      -76     
============================================
  Files           138      138              
  Lines          5256     5256              
  Branches        635      635              
============================================
- Hits           1476     1276     -200     
- Misses         3578     3797     +219     
+ Partials        202      183      -19     

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[atshaw43]

LGTM

For future note, I see we are testing the EntityImpl serialization here.

aws-xray-sdk-java/aws-xray-recorder-sdk-core/src/test/java/com/amazonaws/xray/entities/EntityTest.java

Line 48 in 398ec05

void testTimestampSerialization() {