Update search dev docs for sharding, transfers & deletes
What does this MR do and why?
Related to #471833
It's not possible to create a generic delete worker that uses traversal_ids
since all indexes do not have the field in the document mapping.
This MR updates the development guidelines with how to keep the indexed data consistent when transfers and deletes happen.
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How to set up and validate locally
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Edited by Terri Chu