feat: add parsers for Docling, LlamaCloud, and Unstructured to ETL pipeline

surfsense_backend/app/etl_pipeline/parsers/unstructured.py

@@ -0,0 +1,14 @@
+async def parse_with_unstructured(file_path: str) -> str:
+    from langchain_unstructured import UnstructuredLoader
+
+    loader = UnstructuredLoader(
+        file_path,
+        mode="elements",
+        post_processors=[],
+        languages=["eng"],
+        include_orig_elements=False,
+        include_metadata=False,
+        strategy="auto",
+    )
+    docs = await loader.aload()
+    return "\n\n".join(doc.page_content for doc in docs if doc.page_content)