Don't use '，' (U+FF0C) but ', ' (U+2C U+20) (#8063)

The Unicode codepoint '，' (U+FF0C) is meant to be used in Chinese text,
but this is English text. It looks like a comma followed by a space, but
isn't. Of course I didn't change actual Chinese text.

### What problem does this PR solve?

Mixup of Unicode characters. This is probably unnoticed by most users,
but I wonder if screen readers would read it out differently or if LLMs
would trip up on it.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [ ] New Feature (non-breaking change which adds functionality)
- [x] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Other (please describe):

docs/references/http_api_reference.md

@@ -900,7 +900,7 @@ curl --request PUT \
 - `document_id`: (*Path parameter*)  
   The ID of the document to update.
 - `"name"`: (*Body parameter*), `string`
-- `"meta_fields"`: (*Body parameter*)， `dict[str, Any]` The meta fields of the document.
+- `"meta_fields"`: (*Body parameter*), `dict[str, Any]` The meta fields of the document.
 - `"chunk_method"`: (*Body parameter*), `string`  
   The parsing method to apply to the document:  
   - `"naive"`: General
@@ -2142,7 +2142,7 @@ Success:
         "id": "4606b4ec87ad11efbc4f0242ac120006",
         "messages": [
             {
-                "content": "Hi! I am your assistant，can I help you?",
+                "content": "Hi! I am your assistant, can I help you?",
                 "role": "assistant"
             }
         ],
@@ -2283,7 +2283,7 @@ Success:
             "id": "578d541e87ad11ef96b90242ac120006",
             "messages": [
                 {
-                    "content": "Hi! I am your assistant，can I help you?",
+                    "content": "Hi! I am your assistant, can I help you?",
                     "role": "assistant"
                 }
             ],