docs: Update tutorials to not use bin/post-index-task

[avaamsel]

Updated tutorials to no longer user bin/post-index-task and instead use cURL so users can directly call the Overlord API themselves.

Edited:

• docs/ingestion/native-batch.md
• docs/tutorials/tutorial-batch.md
• docs/tutorials/tutorial-compaction.md
• docs/tutorials/tutorial-delete-data.md
• docs/tutorials/tutorial-ingestion-spec.md
• docs/tutorials/tutorial-retention.md

This PR has:

• been self-reviewed.
• been tested in a test Druid cluster.