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)

web/src/components/document-preview/index.tsx

@@ -82,7 +82,7 @@ const Preview = ({
           <CSVFileViewer className={className} url={url} />
         </section>
       )}
-      {['md'].indexOf(fileType) > -1 && (
+      {['md', 'mdx'].indexOf(fileType) > -1 && (
         <section>
           <Md className={className} url={url} />
         </section>