Adding incremental object storage migration reference architecture diagram (#16776)

* Adding incremental obejct storage migration reference architecture diagram

* Update text for incremental-object-storage-migration.mdx

* Change document title

* Remove blog link

* Update on-demand-object-storage-migration.mdx

Minor language changes for clarity

* Update on-demand-object-storage-migration.mdx

Minor change

* Expand language for large file transfers

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Co-authored-by: Simon Thorpe <[email protected]>

Author: thomas-desmond