[Refactor] Sets util from server to common lib

[nknize]

This simple PR refactors the Sets utility class from the server module to the common library util package.

relates #5910

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/13844/
• CommitID: edc16a0
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
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[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/13845/
• CommitID: edc16a0
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/13851/
• CommitID: ed391e2

[andrross]

Should this retain the @opensearch.internal label now that it is in the common lib?

[nknize]

For now I think it should. I haven't dug deep enough on this to see if this class should stay the way it is. We may want to consider refactoring it to a different utility method or package altogether. Keeping it marked internal will give us that freedom to reasses without guaranteeing bwc.