Write the actual URIs where files are saved to by file sources to a new `uri` field of the `ExportObjectResultMetadata` model. Restore behavior before commit 53012bf, namely setting the history export request metadata before attempting the export.
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Before applying the set of changes from 53012bf, the method `ModelStoreManager.set_history_export_request_metadata()` instantiates a `ExportObjectMetadata` Pydantic model and dumps it to the database in the form of JSON as the field `StoreExportAssociation.export_metadata`. After the export is complete, the method `set_history_export_result_metadata()` takes the same instance of `ExportObjectMetadata`, instantiates a `ExportObjectResultMetadata` Pydantic model, sets it as the `result_data` of the `ExportObjectMetadata` instance, and then saves the `ExportObjectMetadata` Pydantic model in the form of JSON to the database again.
After applying the set of changes, the call to `ModelStoreManager.set_history_export_request_metadata()` is delayed until the file has already been saved to the file source, as the actual URI that the file source assigns to the file is otherwise unknown.
The URI assigned by the file source overwrites the original target URI in the request. This involves a slight deviation from the previous behavior: if for example, power gets cut at the right time, `StoreExportAssociation.export_metadata` may not exist despite the history having been already saved to the file source, because database writes happen within the `finally:` block.
Moreover, overwriting the original target URI from the request is formally wrong, because the actual URI assigned by the file source should be part of the export result metadata, as it becomes known when the export completes.
This commit addresses these issues by adding a new field `uri` to the `ExportObjectResultMetadata` model, where the actual URI the file has been saved to by the file source is written. Backwards compatibility is ensured via `HistoriesService._get_export_record_data()`, which retrieves the new field when available and otherwise uses `ExportObjectRequestMetadata.payload.target_uri` (given that `ExportObjectRequestMetadata.payload` is of type `WriteStoreToPayload`).
Aysam Guerler