Move some constants to common (#11004)

### What problem does this PR solve?

As title.

### Type of change

- [x] Refactoring

---------

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

rag/flow/parser/parser.py

@@ -22,7 +22,7 @@ import trio
 import numpy as np
 from PIL import Image
 
-from api.db import LLMType
+from common.constants import LLMType
 from api.db.services.file2document_service import File2DocumentService
 from api.db.services.file_service import FileService
 from api.db.services.llm_service import LLMBundle

rag/flow/tokenizer/tokenizer.py

@@ -19,7 +19,7 @@ import re
 import numpy as np
 import trio
 
-from api.db import LLMType
+from common.constants import LLMType
 from api.db.services.knowledgebase_service import KnowledgebaseService
 from api.db.services.llm_service import LLMBundle
 from api.db.services.user_service import TenantService