Add "Not used anywhere" option to the Used In filter

[gabrieldagama]

Story: #1059

Add a new option to the Used in filter to allow users to filter assets that are not used anywhere. The desired behavior here is the search to return assets that have no relationship with content (product, page, blocks, and categories).

Technical details
https://github.com/magento/adobe-stock-integration/wiki/MediaGalleryUi-DataProvider

[m2-assistant]

Hi @gabrieldagama. Thank you for your report.
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