Changes to Create a post

added the new optional request property posts/items/settings/oneOf[subschema #15: Dev.to]/main_image/thumbnailTimestamp

added the new optional request property posts/items/settings/oneOf[subschema #16: Hashnode]/main_image/thumbnailTimestamp

added the new optional request property posts/items/settings/oneOf[subschema #17: WordPress]/main_image/thumbnailTimestamp

added the new optional request property posts/items/settings/oneOf[subschema #5: YouTube]/thumbnail/thumbnailTimestamp

added the new optional request property posts/items/value/items/image/items/thumbnailTimestamp