[Backport 2.x] Added empty build.gradle files for arm64 and s390x because the gradle assemble task fails without them

[opensearch-trigger-bot]

Backport 0003bd8 from #8904.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      2 org.opensearch.search.SearchWeightedRoutingIT.testStrictWeightedRoutingWithCustomString

• URL: https://build.ci.opensearch.org/job/gradle-check/21268/
• CommitID: c8cf4b3
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Merging #8964 (c8cf4b3) into 2.x (c1d4b3d) will increase coverage by 0.06%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.x    #8964      +/-   ##
============================================
+ Coverage     70.75%   70.81%   +0.06%     
- Complexity    57312    57408      +96     
============================================
  Files          4745     4745              
  Lines        271092   271092              
  Branches      39988    39988              
============================================
+ Hits         191810   191978     +168     
+ Misses        62814    62687     -127     
+ Partials      16468    16427      -41     

see 471 files with indirect coverage changes