Fix deprecation warning in data node

[moesterheld]

Description

Calls to data node's Opensearch endpoint _nodes show a deprecation warning in the logs. This change removes this deprecation warning.

/nocl internal change

Motivation and Context

fixes #20759

How Has This Been Tested?

Startup data node without this change
-> any call to _nodes from Graylog will show warning in Graylog logs
alternatively, call /api/datanodes/any/opensearch/_nodes endpoint directly, check Graylog logs

Startup data node with change
-> no warning is shown

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[todvora]

LGTM, thanks!