Move some constants to common (#11004)

### What problem does this PR solve?

As title.

### Type of change

- [x] Refactoring

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

agent/tools/retrieval.py

@@ -19,7 +19,7 @@ import os
 import re
 from abc import ABC
 from agent.tools.base import ToolParamBase, ToolBase, ToolMeta
-from api.db import LLMType
+from common.constants import LLMType
 from api.db.services.document_service import DocumentService
 from api.db.services.dialog_service import meta_filter
 from api.db.services.knowledgebase_service import KnowledgebaseService