feat: add MDX file support (#12261)

Feat: add MDX file support  #12057 
### What problem does this PR solve?

<img width="1055" height="270" alt="image"
src="https://github.com/user-attachments/assets/a0ab49f9-7806-41cd-8a96-f593591ab36b"
/>

The page states that MDX files are supported, but uploading fails with
the error: "x.mdx: This type of file has not been supported yet!"
<img width="381" height="110" alt="image"
src="https://github.com/user-attachments/assets/4bbb7d08-cb47-416a-95fc-bc90b90fcc39"
/>


### Type of change

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

api/utils/web_utils.py

@@ -69,6 +69,7 @@ CONTENT_TYPE_MAP = {
     # Web
     "md": "text/markdown",
     "markdown": "text/markdown",
+    "mdx": "text/markdown",
     "htm": "text/html",
     "html": "text/html",
     "json": "application/json",