Derivative Unit field should not present in OpenSearch Query if unit field is not set in Visualisation

[kalaivani61294]

Describe the bug

Derivative Unit field should not present in OpenSearch Query if unit field is not set in Visualisation

To Reproduce Steps to reproduce the behaviour:

1. configure the derivative aggregation with unit value as empty
2. Then, please check the open search query value will have unit field as same as intervalString configured

Expected behavior Derivative Unit field should not present in OpenSearch Query if unit field is not set in Visualisation

OpenSearch Version opensearch-1.2.4

Dashboards Version opensearch-1.2.0

Screenshots

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Host/Environment (please complete the following information):

• MAC OS
• CHROME Version 124.0.6367.119 (Official Build) (arm64)

Additional context

Add any other context about the problem here.

[abbyhu2000]

@kavilla to reproduce the bug