Add MIME types for PPT and PPTX files (#12562)

Otherwise, slide files cannot be opened in Chat module

### What problem does this PR solve?

Backend Reason (API): In the api/utils/web_utils.py file of the backend,
the CONTENT_TYPE_MAP dictionary is missing ppt and pptx.
MIME type mapping. This means that when the frontend requests a PPTX
file, the backend cannot correctly inform the browser that it is a PPTX
file, resulting in the file being displayed incorrectly.
Type identification error.

### Type of change

-  Bug Fix (non-breaking change which fixes an issue)

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: LiruiYu33

api/utils/web_utils.py

@@ -86,6 +86,9 @@
     "ico": "image/x-icon",
     "avif": "image/avif",
     "heic": "image/heic",
+    # PPTX
+    "ppt": "application/vnd.ms-powerpoint",
+    "pptx": "application/vnd.openxmLformats-officedocument.presentationml.presentation",
 }
 
 
@@ -239,4 +242,4 @@ def hash_code(code: str, salt: bytes) -> str:
 
 def captcha_key(email: str) -> str:
     return f"captcha:{email}"
-    
+