Add $comment as a NonValidationKeyword for v7 and v2019 drafts

[kmalski]

I am not sure I am able to test this change. I did not find out any idea how to do it 😄

You can find the reference to the schema here:
https://json-schema.org/understanding-json-schema/reference/generic.html#comments
and here:
https://json-schema.org/draft-07/json-schema-core.html#rfc.section.9

[codecov-commenter]

Codecov Report

Merging #328 into master will increase coverage by 0.18%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #328      +/-   ##
============================================
+ Coverage     70.79%   70.97%   +0.18%     
- Complexity      652      653       +1     
============================================
  Files            75       75              
  Lines          2496     2491       -5     
  Branches        529      529              
============================================
+ Hits           1767     1768       +1     
+ Misses          525      520       -5     
+ Partials        204      203       -1     

Impacted Files	Coverage Δ	Complexity Δ
...main/java/com/networknt/schema/JsonMetaSchema.java	85.82% <ø> (+2.48%)	16.00 <0.00> (ø)
...a/com/networknt/schema/format/DomainValidator.java	24.44% <0.00%> (+0.17%)	16.00% <0.00%> (ø%)
...n/java/com/networknt/schema/JsonSchemaFactory.java	77.77% <0.00%> (+0.61%)	31.00% <0.00%> (+1.00%)

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[stevehu]

I don't think we need a test case for this as long as you don't see the warning message from the log. Thanks a lot for your help.