[improve] Upgrade opensearch sink to client 2.16 and tests to use server 2.16.0

[dlg99]

Motivation

Upgrade opensearch sink to client 2.16 and tests to use server 2.16.0

Modifications

Upgraded opensearch sink to client 2.16 and updated tests to use server 2.16.0

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

NO

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API: (yes / no)
• The schema: (yes / no / don't know)
• The default values of configurations: (yes / no)
• The wire protocol: (yes / no)
• The rest endpoints: (yes / no)
• The admin cli options: (yes / no)
• Anything that affects deployment: (yes / no / don't know)

Documentation

Check the box below or label this PR directly (if you have committer privilege).

Need to update docs?

• doc-required

  (If you need help on updating docs, create a doc issue)

• no-need-doc

  (Please explain why)

• doc

  (If this PR contains doc changes)