fix: change default minimum log level to TRACE

[imbajin]

Log4j2 has 8 log levels: ALL < TRACE < DEBUG < INFO < WARN < ERROR < FATAL < OFF (from low to high)

1. change minimum level from INFO to TRACE to allow print DEBUG & TRACE log
2. change graph/*API Log print class to themselves instead of RestServer.class

And we lack TRACE level logs now, so that the DEBUG output is too much (almost can't be directly opened)

My temporary solution is to dynamically modify the log level of specified classes to DEBUG through Arthas like this:

# 1.Change the same prefix classes log level together
$ logger -n com.baidu.hugegraph.api.graph -l debug

# 2.Only change one class
$ logger -n com.baidu.hugegraph.api.graph.VertexAPI -l debug

That's why we should let different class print its own logs separately(especially for thoses output a lot of logs), otherwise we have to change RestServer.class to debug, and it will print a lot of useless log.

[codecov]

Codecov Report

Merging #1050 into master will increase coverage by 2.77%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #1050      +/-   ##
============================================
+ Coverage     66.38%   69.16%   +2.77%     
- Complexity     5295     5445     +150     
============================================
  Files           329      329              
  Lines         26424    26424              
  Branches       3776     3776              
============================================
+ Hits          17542    18276     +734     
+ Misses         7151     6363     -788     
- Partials       1731     1785      +54     

Impacted Files	Coverage Δ	Complexity Δ
...n/java/com/baidu/hugegraph/api/graph/BatchAPI.java	27.41% <100.00%> (+1.61%)	0.00 <0.00> (ø)
...in/java/com/baidu/hugegraph/api/graph/EdgeAPI.java	54.68% <100.00%> (ø)	0.00 <0.00> (ø)
.../java/com/baidu/hugegraph/api/graph/VertexAPI.java	36.80% <100.00%> (ø)	0.00 <0.00> (ø)
...om/baidu/hugegraph/api/filter/ExceptionFilter.java	64.28% <0.00%> (-4.09%)	0.00% <0.00%> (ø%)
...c/main/java/com/baidu/hugegraph/task/HugeTask.java	69.76% <0.00%> (-0.34%)	69.00% <0.00%> (-1.00%)
...graph/backend/store/cassandra/CassandraTables.java	88.14% <0.00%> (+0.26%)	3.00% <0.00%> (ø%)
...om/baidu/hugegraph/task/StandardTaskScheduler.java	85.61% <0.00%> (+0.35%)	67.00% <0.00%> (ø%)
...egraph/backend/store/cassandra/CassandraStore.java	69.01% <0.00%> (+0.35%)	53.00% <0.00%> (+1.00%)
.../baidu/hugegraph/backend/query/ConditionQuery.java	86.20% <0.00%> (+0.43%)	101.00% <0.00%> (+1.00%)
.../hugegraph/backend/serializer/TableSerializer.java	87.90% <0.00%> (+0.53%)	61.00% <0.00%> (+1.00%)
... and 23 more

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