[LIVY-990][SERVER] Persisting Livy Statements

[askhatri]

What changes were proposed in this pull request?

Persisting Livy Statements into files to generate statement history logs for auditing purpose.

JIRA: https://issues.apache.org/jira/browse/LIVY-990

How was this patch tested?

Tested manually by creating statements in Livy interactive session.

[codecov-commenter]

Codecov Report

Merging #423 (527a273) into master (8b2e29f) will decrease coverage by 36.90%.
The diff coverage is 47.22%.

@@              Coverage Diff              @@
##             master     #423       +/-   ##
=============================================
- Coverage     65.48%   28.59%   -36.90%     
+ Complexity      950      382      -568     
=============================================
  Files           103      104        +1     
  Lines          6062     6098       +36     
  Branches        916      920        +4     
=============================================
- Hits           3970     1744     -2226     
- Misses         1541     3997     +2456     
+ Partials        551      357      -194     

Files	Coverage Δ
...rver/src/main/scala/org/apache/livy/LivyConf.scala	95.30% <100.00%> (+1.01%)	⬆️
...e/livy/server/interactive/InteractiveSession.scala	71.32% <100.00%> (+9.10%)	⬆️
...pache/livy/server/interactive/StatementStore.scala	34.48% <34.48%> (ø)

... and 84 files with indirect coverage changes

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