[Backport 2.x] Added SIGNUM function to V2 engine

[opensearch-trigger-bot]

Backport 6496692 from #1429

[codecov-commenter]

Codecov Report

Merging #1442 (e56af86) into 2.x (014de25) will increase coverage by 0.00%.
The diff coverage is 100.00%.

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@@            Coverage Diff            @@
##                2.x    #1442   +/-   ##
=========================================
  Coverage     98.38%   98.38%           
- Complexity     3702     3705    +3     
=========================================
  Files           343      343           
  Lines          9125     9130    +5     
  Branches        582      582           
=========================================
+ Hits           8978     8983    +5     
  Misses          142      142           
  Partials          5        5           

Flag	Coverage Δ
sql-engine	98.38% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...c/main/java/org/opensearch/sql/expression/DSL.java	100.00% <100.00%> (ø)
...h/sql/expression/function/BuiltinFunctionName.java	100.00% <100.00%> (ø)
...ssion/operator/arthmetic/MathematicalFunction.java	100.00% <100.00%> (ø)

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[dai-chen]

Failed on a IT. Retrying

2023-03-15T21:19:28.6355767Z   2> REPRODUCE WITH: ./gradlew ':integ-test:integTest' --tests "org.opensearch.sql.ppl.PrometheusDataSourceCommandsIT.testSourceMetricCommandWithTimestamp" -Dtests.seed=8556746038C8F76E -Dtests.security.manager=false -Dtests.locale=hi-IN -Dtests.timezone=Africa/Lome -Druntime.java=17
2023-03-15T21:19:28.6356466Z         "reason": "Invalid Query",
2023-03-15T21:19:28.6357489Z   2> org.opensearch.client.ResponseException: method [POST], host [http://127.0.0.1:36873], URI [/_plugins/_ppl], status line [HTTP/1.1 400 Bad Request]
2023-03-15T21:19:28.6376325Z         "details": "timestamp:२०२३-०३-१५ २०:१९:२८ in unsupported format, please use yyyy-MM-dd HH:mm:ss[.SSSSSSSSS]",
2023-03-15T21:19:28.6376825Z     {
2023-03-15T21:19:28.6377011Z       "error": {
2023-03-15T21:19:28.6377223Z         "reason": "Invalid Query",
2023-03-15T21:19:28.6377809Z         "details": "timestamp:२०२३-०३-१५ २०:१९:२८ in unsupported format, please use yyyy-MM-dd HH:mm:ss[.SSSSSSSSS]",
2023-03-15T21:19:28.6378167Z         "type": "SemanticCheckException"
2023-03-15T21:19:28.6378438Z       },
2023-03-15T21:19:28.6378618Z       "status": 400
2023-03-15T21:19:28.6378829Z     }