Fix the type of default values to match what Schema.parse() does.

[srramach]

When calling field.defaultVal() (or equivalent compat helper methods)
under Avro 1.9.2+, we get back a type that's not consistent with what
Schema.parse() creates internally. This causes two Schemas constructed
in these two different ways (Schema.parse vs Schema.createRecord) to
be considered unequal, even though their toString() representations
are identical.

Fix this situation by calling parseJsonToObject(), which results in
the default value being interpreted similar to Schema.parse().

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JIRA

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[codecov-commenter]

Codecov Report

Merging #3611 (4240794) into master (c6d6c1b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master    #3611   +/-   ##
=========================================
  Coverage     46.87%   46.88%           
+ Complexity    10687    10684    -3     
=========================================
  Files          2125     2125           
  Lines         83157    83157           
  Branches       9266     9266           
=========================================
+ Hits          38983    38987    +4     
+ Misses        40598    40590    -8     
- Partials       3576     3580    +4     

Impacted Files	Coverage Δ
...c/main/java/org/apache/gobblin/util/AvroUtils.java	56.50% <100.00%> (ø)
...e/gobblin/service/monitoring/GitConfigMonitor.java	95.23% <0.00%> (-4.77%)	⬇️
...a/org/apache/gobblin/cluster/GobblinHelixTask.java	62.36% <0.00%> (-2.16%)	⬇️
...a/management/copy/publisher/CopyDataPublisher.java	74.17% <0.00%> (-1.33%)	⬇️
...anagement/copy/replication/ConfigBasedDataset.java	68.87% <0.00%> (ø)
...main/java/org/apache/gobblin/yarn/YarnService.java	15.68% <0.00%> (+0.65%)	⬆️
.../gobblin/util/limiter/BatchedPermitsRequester.java	75.47% <0.00%> (+0.75%)	⬆️
.../gobblin/cluster/GobblinHelixTaskStateTracker.java	68.75% <0.00%> (+6.25%)	⬆️
...he/gobblin/source/PartitionAwareFileRetriever.java	55.55% <0.00%> (+7.40%)	⬆️

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