Implement Delete in GO and refactor functions (#13974)

### What problem does this PR solve?

Implement Delete in GO and refactor functions

### Type of change

- [x] Refactoring

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added a remove_chunks command to delete specific or all chunks from a
document.
  * Added new endpoints for chunk removal and chunk update.

* **Refactor**
* Renamed index commands to dataset/metadata table terminology and
updated REST routes accordingly.
* Updated chunk update flow to a JSON POST style and improved metadata
error messages.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

internal/handler/document.go

@@ -22,6 +22,7 @@ import (
 	"net/http"
 	"ragflow/internal/common"
 	"strconv"
+	"strings"
 
 	"github.com/gin-gonic/gin"
 
@@ -461,10 +462,18 @@ func (h *DocumentHandler) SetMeta(c *gin.Context) {
 
 	err := h.documentService.SetDocumentMetadata(req.DocID, meta)
 	if err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{
-			"code":    1,
-			"message": "Failed to set metadata: " + err.Error(),
-		})
+		errMsg := err.Error()
+		if strings.Contains(errMsg, "no such document") || strings.Contains(errMsg, "document not found") {
+			c.JSON(http.StatusBadRequest, gin.H{
+				"code":    1,
+				"message": errMsg,
+			})
+		} else {
+			c.JSON(http.StatusInternalServerError, gin.H{
+				"code":    1,
+				"message": "Failed to set metadata: " + errMsg,
+			})
+		}
 		return
 	}