create imported asset directory if needed (bevyengine#9716)

# Objective

- Related to bevyengine#9715 
- Example `asset_processing` logs the following error:
```
thread 'IO Task Pool (1)' panicked at 'Failed to initialize asset processor log. This cannot be recovered. Try restarting. If that doesn't work, try deleting processed asset folder. No such file or directory (os error 2)', crates/bevy_asset/src/processor/mod.rs:867:25
```

## Solution

- Create the log directory if needed

---------

Co-authored-by: Carter Anderson <mcanders1@gmail.com>

crates/bevy_asset/src/processor/log.rs

@@ -89,6 +89,10 @@ impl ProcessorTransactionLog {
             }
         }
 
+        if let Some(parent_folder) = path.parent() {
+            async_fs::create_dir_all(parent_folder).await?;
+        }
+
         Ok(Self {
             log_file: File::create(path).await?,
         })