Fix bug: broken import from rag.prompts.prompts (#10217)

### What problem does this PR solve?

Fix broken imports

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

---------

Signed-off-by: jinhai <haijin.chn@gmail.com>

rag/prompts/__init__.py

@@ -1,6 +1,6 @@
-from . import prompts
+from . import generator
 
-__all__ = [name for name in dir(prompts)
+__all__ = [name for name in dir(generator)
            if not name.startswith('_')]
 
-globals().update({name: getattr(prompts, name) for name in __all__})
+globals().update({name: getattr(generator, name) for name in __all__})