Added semi-automatic mode to the metadata filter (#11886)

### What problem does this PR solve?

Retrieval metadata filtering adds semi-automatic mode, and users can
manually check the metadata key that participates in LLM to generate
filter conditions.
### Type of change

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

web/src/constants/chat.ts

@@ -36,5 +36,6 @@ export const EmptyConversationId = 'empty';
 export enum DatasetMetadata {
   Disabled = 'disabled',
   Automatic = 'auto',
+  SemiAutomatic = 'semi_auto',
   Manual = 'manual',
 }