make CrdtElements and Operations data class.

[skhugh]

What this PR does / why we need it?

made some misc improvements.
make CrdtElements and Operations data class for better copying and constructions.
fix authInterceptor null issue.

Any background context you want to provide?

What are the relevant tickets?

Fixes #

Checklist

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Merging #40 (d785465) into main (e18bfe2) will decrease coverage by 0.21%.
The diff coverage is 79.59%.

@@             Coverage Diff              @@
##               main      #40      +/-   ##
============================================
- Coverage     75.65%   75.43%   -0.22%     
+ Complexity      369      366       -3     
============================================
  Files            43       43              
  Lines          1614     1657      +43     
  Branches        230      233       +3     
============================================
+ Hits           1221     1250      +29     
- Misses          259      273      +14     
  Partials        134      134              

Impacted Files	Coverage Δ
...src/main/kotlin/dev/yorkie/core/AuthInterceptor.kt	10.00% <0.00%> (-2.50%)	⬇️
...kotlin/dev/yorkie/document/crdt/CrdtTextElement.kt	0.00% <0.00%> (ø)
...c/main/kotlin/dev/yorkie/document/crdt/RhtPQMap.kt	79.71% <0.00%> (-4.91%)	⬇️
.../main/kotlin/dev/yorkie/document/json/JsonArray.kt	59.25% <0.00%> (ø)
...src/main/kotlin/dev/yorkie/api/ElementConverter.kt	55.47% <47.61%> (-1.57%)	⬇️
...ie/src/main/kotlin/dev/yorkie/util/SplayTreeSet.kt	77.18% <66.66%> (ø)
...ain/kotlin/dev/yorkie/document/crdt/RgaTreeList.kt	76.63% <82.75%> (-2.37%)	⬇️
...ain/kotlin/dev/yorkie/document/crdt/CrdtElement.kt	77.77% <83.33%> (-8.89%)	⬇️
...ain/kotlin/dev/yorkie/document/crdt/CrdtCounter.kt	90.00% <92.30%> (ø)
...ie/src/main/kotlin/dev/yorkie/document/Document.kt	86.59% <100.00%> (ø)
... and 18 more

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[hackerwins]

Thanks for your contribution. 👍