Fix issue in testSourceMetricCommandWithTimestamp integ test with different timezones and locales.

[vamsi-amazon]

Description

[Describe what this change achieves]
Switched to LocalDateTime for better handling of timezone and locale.
It uses system timezone irrespective of timezone set in JVM using -Dtests.locale=hi-IN -Dtests.timezone=America/Atka.

Error before fix.

timestamp:२०२४-०२-१६ १०:१७:४७ in unsupported format

Testing

Following commands worked without error.

./gradlew ':integ-test:integTest' --tests "org.opensearch.sql.ppl.PrometheusDataSourceCommandsIT.testSourceMetricCommandWithTimestamp" -Dtests.seed=1574D2ADC54025EE -Dtests.security.manager=false -Dtests.locale=ja-JP-u-ca-japanese-x-lvariant-JP -Dtests.timezone=VST

./gradlew ':integ-test:integTest' --tests "org.opensearch.sql.ppl.PrometheusDataSourceCommandsIT.testSourceMetricCommandWithTimestamp" -Dtests.seed=EE70DA8B4C47EEC -Dtests.security.manager=false -Dtests.locale=hi-IN -Dtests.timezone=America/Atka

Issues Resolved

#1275
#2517

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[noCharger]

Nice!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cddffc6) 95.41% compared to head (b18ec13) 95.41%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #2522   +/-   ##
=========================================
  Coverage     95.41%   95.41%           
  Complexity     5027     5027           
=========================================
  Files           483      483           
  Lines         14016    14016           
  Branches        944      944           
=========================================
  Hits          13374    13374           
  Misses          621      621           
  Partials         21       21           

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[vamsi-amazon]

bwc tests are unrelated.