Document the Delete Task API

[cwperks]

Description

Adds API documentation for the Delete Task API introduced by opensearch-project/OpenSearch#21727.

The new page explains how to delete stored completed task results, distinguishes deletion from task cancellation, documents common response codes, and describes the leaf-first deletion requirement for parent and child task results. It also places the new page in the Tasks APIs navigation.

Issues Resolved

Documents opensearch-project/OpenSearch#21727.

Version

3.8

Frontend features

Not applicable.

Checklist

• By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and subject to the Developers Certificate of Origin.

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[kolchfa-aws]

Thanks, @cwperks! Doc review complete and changes applied. Version changed to 3.9. Please let me know when you add the API spec for this so I can regenerate the appropriate sections. Thanks!

[cwperks]

Thanks, @cwperks! Doc review complete and changes applied. Version changed to 3.9. Please let me know when you add the API spec for this so I can regenerate the appropriate sections. Thanks!

I will create this later today.

[cwperks]

The API specification PR is now open: https://github.com/opensearch-project/opensearch-api-specification/pull/1215\n\nIt adds the OpenSearch 3.9 delete-task operation, acknowledged response schema, and a focused Tasks story that passed locally against OpenSearch 3.9.0-SNAPSHOT.