feat: implement and test index method

surfsense_backend/app/indexing_pipeline/document_chunker.py

@@ -0,0 +1,6 @@
+from app.config import config
+
+
+def chunk_text(text: str) -> list[str]:
+    """Chunk a text string using the configured chunker and return the chunk texts."""
+    return [c.text for c in config.chunker_instance.chunk(text)]