[FEATURE] Add missing Integration test for PPL integration with MLCommons

[dhrubo-os]

Is your feature request related to a problem?
Right now PPL integration with MLCommons doesn't have any corresponding integration test.

In 2.7, we found out that the following query was breaking to execute:

POST _plugins/_ppl
{
  "query": "source=iris_data | fields petal_length_in_cm,petal_width_in_cm | kmeans centroids=3"
}

Details in this PR

This error should caught up during integration testing.

What solution would you like?
Need to write corresponding Integration test.