Flaky test fix

[bowenlan-amzn]

Description

Summary

• Fix flaky test test multi-tier rollup with cardinality in RollupActionIT

Test plan

• Verified test passes with the previously failing seed:

./gradlew ':integTest' --tests 'org.opensearch.indexmanagement.indexstatemanagement.action.RollupActionIT.test multi-tier rollup with cardinality' -Dtests.seed=B2B48E214ECA5C1 -Dtests.security.manager=false -Dtests.locale=dz-BT -Dtests.timezone=Etc/GMT-6

• Verified all RollupActionIT tests pass

Issue

The test was flaky when running with certain locales (e.g., dz-BT Dzongkha/Bhutan).

Root cause: String.format("%02d", ...) produces locale-specific digits. In the Dzongkha locale, this outputs Tibetan numerals (༠༡, ༠༢, etc.) instead of ASCII digits (01, 02, etc.). This caused timestamps like 2024-01-01T༠༡:00:00Z to fail ISO 8601 date parsing, resulting in all bulk index operations failing silently.

Changes

1. Use Locale.ROOT for timestamp formatting - Ensures ASCII digits are always used regardless of test locale
2. Add bulk response error checking - Fails fast if bulk indexing encounters errors, making future issues easier to diagnose
3. Create index before attaching ISM policy - Prevents potential race condition where ISM could start processing before data is indexed

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.50%. Comparing base (ffe568f) to head (1718ac1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1574      +/-   ##
==========================================
+ Coverage   76.39%   76.50%   +0.11%     
==========================================
  Files         381      381              
  Lines       18058    18058              
  Branches     2501     2501              
==========================================
+ Hits        13796    13816      +20     
+ Misses       2991     2974      -17     
+ Partials     1271     1268       -3     

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