add string function RIGHT

[rupal-bq]

Description of changes:

• Added string function RIGHT().
• Added unit test.
• Added manual IT because the comparison test didn't work.
• Updated doc.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Merging #938 (c7a0170) into develop (c377026) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             develop     #938   +/-   ##
==========================================
  Coverage      99.86%   99.86%           
- Complexity      2315     2337   +22     
==========================================
  Files            230      232    +2     
  Lines           5329     5383   +54     
  Branches         346      350    +4     
==========================================
+ Hits            5322     5376   +54     
  Misses             5        5           
  Partials           2        2           

Impacted Files	Coverage Δ	Complexity Δ
...opendistroforelasticsearch/sql/expression/DSL.java	100.00% <100.00%> (ø)	129.00 <1.00> (+1.00)
...h/sql/expression/function/BuiltinFunctionName.java	100.00% <100.00%> (ø)	3.00 <0.00> (ø)
...lasticsearch/sql/expression/text/TextFunction.java	100.00% <100.00%> (ø)	34.00 <2.00> (+2.00)
.../sql/elasticsearch/storage/ElasticsearchIndex.java	100.00% <0.00%> (ø)	3.00% <0.00%> (ø%)
.../elasticsearch/storage/ElasticsearchIndexScan.java	100.00% <0.00%> (ø)	19.00% <0.00%> (+1.00%)
...ch/planner/logical/rule/OptimizationRuleUtils.java	100.00% <0.00%> (ø)	9.00% <0.00%> (+3.00%)
...planner/logical/ElasticsearchLogicalIndexScan.java	100.00% <0.00%> (ø)	7.00% <0.00%> (+3.00%)
...ical/ElasticsearchLogicalPlanOptimizerFactory.java	100.00% <0.00%> (ø)	1.00% <0.00%> (ø%)
...h/planner/logical/rule/PushProjectAndRelation.java	100.00% <0.00%> (ø)	5.00% <0.00%> (?%)
.../planner/logical/rule/PushProjectAndIndexScan.java	100.00% <0.00%> (ø)	7.00% <0.00%> (?%)

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[dai-chen]

Thanks for the changes! Could you check if we can add comparison test now? https://github.com/opendistro-for-elasticsearch/sql/tree/develop/integ-test/src/test/resources/correctness/expressions

I recall there was some issue adding text function. I think it's doable now?

[penghuo]

could you also add the doc for PPL? https://github.com/opendistro-for-elasticsearch/sql/blob/develop/docs/experiment/ppl/functions/string.rst

[rupal-bq]

Thanks for the changes! Could you check if we can add comparison test now? https://github.com/opendistro-for-elasticsearch/sql/tree/develop/integ-test/src/test/resources/correctness/expressions

I recall there was some issue adding text function. I think it's doable now?

Thanks. added comparison test.

[rupal-bq]

could you also add the doc for PPL? https://github.com/opendistro-for-elasticsearch/sql/blob/develop/docs/experiment/ppl/functions/string.rst

Thanks. added this change.