fix(plugin-cloud-storage): should persist external data returned by handleUpload (#15188)

### What
Fixes issue where storage metadata (object keys, timestamps, custom IDs,
etc.) from external providers (s3, azure, etc) is no longer persisted
back to the main doc. This issue was introduced in PR #14988 when the
external upload process was moved from the `beforeChange` to
`afterChange` hook.

### Why
Without automatically persisting metadata from external storage, users
have to manually update the doc themselves. This restores backward
compatibility for existing custom storage adapters.

### Where
Added automatic data capture/persistence in
`packages/plugin-cloud-storage/src/hooks/afterChange`

#### Testing
Added to test suite `test/plugin-cloud-storage`