[DOC] Update delete API in ML

[ylwu-amzn]

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Add exception details for ML APIs: delete API will throw not found exception (404) if model/agent not exist.

User (like FlowFramework team) read our API document and they don't see exception details of delete APIs (delete connector/model group/model/agent etc). So they thought the delete API will not throw error if resource not found.
But actually we are following the same style of OpenSearch core, when user delete a non-existing document, 404 error will return

*Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.

[hdhalter]

@ylwu-amzn , is this related to 2.16?

[ylwu-amzn]

This is not for 2.16 release. @b4sjoo Sicheng, can you help on this ?