Fix IT on 2.x - address breaking changes from upstream.

[Yury-Fridlyand]

Description

IT fails on 2.x branch (can't compile)

2023-05-25T18:49:40.0119575Z /home/runner/work/sql/sql/integ-test/src/test/java/org/opensearch/sql/legacy/OpenSearchSQLRestTestCase.java:36: error: package org.opensearch.core.internal.io does not exist
2023-05-25T18:49:40.0120005Z 
2023-05-25T18:49:40.0120688Z import org.opensearch.core.internal.io.IOUtils;

caused by opensearch-project/OpenSearch#7612
Fortunately, it is a simple fix.

on main it was fixed in scope of #1512, but this specific fix wasn't backported.

Issues Resolved

Fix CI on 2.x

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

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[codecov]

Codecov Report

Merging #1659 (f3670d2) into 2.x (3683b6c) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##                2.x    #1659   +/-   ##
=========================================
  Coverage     97.16%   97.16%           
  Complexity     4122     4122           
=========================================
  Files           371      371           
  Lines         10375    10375           
  Branches        704      704           
=========================================
  Hits          10081    10081           
  Misses          287      287           
  Partials          7        7           

Flag	Coverage Δ
sql-engine	97.16% <ø> (ø)

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