add support for novita.ai (#1910)

### What problem does this PR solve?

#1853  add support for novita.ai

### Type of change


- [x] New Feature (non-breaking change which adds functionality)

---------

Co-authored-by: Zhedong Cen <cenzhedong2@126.com>

api/db/db_models.py

@@ -532,8 +532,7 @@ class LLM(DataBaseModel):
         max_length=128,
         null=False,
         help_text="LLM name",
-        index=True,
-        primary_key=True)
+        index=True)
     model_type = CharField(
         max_length=128,
         null=False,
@@ -558,6 +557,7 @@ class LLM(DataBaseModel):
         return self.llm_name
 
     class Meta:
+        primary_key = CompositeKey('fid', 'llm_name')
         db_table = "llm"
 
 
@@ -965,3 +965,8 @@ def migrate_db():
             )
         except Exception as e:
             pass
+        try:
+            DB.execute_sql('ALTER TABLE llm DROP PRIMARY KEY;')
+            DB.execute_sql('ALTER TABLE llm ADD PRIMARY KEY (llm_name,fid);')
+        except Exception as e:
+            pass