Feat: Markdown add image (#7124)

### What problem does this PR solve?

https://github.com/infiniflow/ragflow/issues/6984

1. Markdown parser supports get pictures
2. For Native, when handling Markdown, it will handle images
3. improve merge and 

### Type of change

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

---------

Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>

web/src/interfaces/database/knowledge.ts

@@ -103,7 +103,7 @@ export interface IChunk {
   content_with_weight: string;
   doc_id: string;
   doc_name: string;
-  img_id: string;
+  image_id: string;
   important_kwd?: string[];
   question_kwd?: string[]; // keywords
   tag_kwd?: string[];

web/src/pages/add-knowledge/components/knowledge-chunk/components/chunk-card/index.tsx

@@ -64,14 +64,14 @@ const ChunkCard = ({
     >
       <Flex gap={'middle'} justify={'space-between'}>
         <Checkbox onChange={handleCheck} checked={checked}></Checkbox>
-        {item.img_id && (
+        {item.image_id && (
           <Popover
             placement="right"
             content={
-              <Image id={item.img_id} className={styles.imagePreview}></Image>
+              <Image id={item.image_id} className={styles.imagePreview}></Image>
             }
           >
-            <Image id={item.img_id} className={styles.image}></Image>
+            <Image id={item.image_id} className={styles.image}></Image>
           </Popover>
         )}