Fix build errors after refactoring of Strings class in core

[Hailong-am]

Description

Fix build break due to refactoring of Strings in core
opensearch-project/OpenSearch#7508

Issues Resolved

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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[codecov]

Codecov Report

Merging #432 (ffe4228) into main (968a23d) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #432   +/-   ##
=========================================
  Coverage     72.87%   72.87%           
  Complexity      712      712           
=========================================
  Files           113      113           
  Lines          4711     4711           
  Branches        606      606           
=========================================
  Hits           3433     3433           
  Misses         1024     1024           
  Partials        254      254           

Impacted Files	Coverage Δ
...in/java/org/opensearch/commons/InjectSecurity.java	71.92% <ø> (ø)
...earch/commons/authuser/AuthUserRequestBuilder.java	0.00% <ø> (ø)
...ain/java/org/opensearch/commons/authuser/User.java	87.82% <ø> (ø)
...commons/destination/message/LegacyBaseMessage.java	67.44% <ø> (ø)
...ommons/destination/message/LegacyChimeMessage.java	89.47% <ø> (ø)
...estination/message/LegacyCustomWebhookMessage.java	74.68% <ø> (ø)
...ommons/destination/message/LegacyEmailMessage.java	89.47% <ø> (ø)
.../commons/destination/message/LegacySNSMessage.java	0.00% <ø> (ø)
...ommons/destination/message/LegacySlackMessage.java	85.71% <ø> (ø)
.../org/opensearch/commons/destination/util/Util.java	0.00% <ø> (ø)
... and 15 more