Fix: Use FileResponse for file API responses (#12638)

* Updates code to use a FileResponse for streaming and unlink the file, but keep a handle to it

* Transitions the rest of the code to use FileResponse instead of a basic response, fixes up tests which assumed .content exists

* While here, let's add schema for it

src/documents/tests/utils.py

@@ -17,6 +17,7 @@ import pytest
 from django.apps import apps
 from django.db import connection
 from django.db.migrations.executor import MigrationExecutor
+from django.http import StreamingHttpResponse
 from django.test import TransactionTestCase
 from django.test import override_settings
 
@@ -150,6 +151,13 @@ def util_call_with_backoff(
     return succeeded, result
 
 
+def read_streaming_response(response: StreamingHttpResponse) -> bytes:
+    """Consume a StreamingHttpResponse/FileResponse and close it."""
+    content = b"".join(response.streaming_content)
+    response.close()
+    return content
+
+
 class DirectoriesMixin:
     """
     Creates and overrides settings for all folders and paths, then ensures