fix(oas3): show request body description for file upload content types

When a request body uses a content type like application/octet-stream
that triggers file upload mode, the description from the requestBody
object was not being displayed. Instead, only the "Example values are
not available" message was shown (in non-execute mode) or just the
file input (in execute mode).

This renders the requestBody description above the file input or
the example-not-available message, consistent with how descriptions
are shown for other content types.

Fixes #5637

Author: yogeshwaran-c

src/core/plugins/oas3/components/request-body.jsx

@@ -114,12 +114,22 @@ const RequestBody = ({
     const Input = getComponent("Input")
 
     if(!isExecute) {
-      return <i>
-        Example values are not available for <code>{contentType}</code> media types.
-      </i>
+      return <div>
+        { requestBodyDescription &&
+          <Markdown source={requestBodyDescription} />
+        }
+        <i>
+          Example values are not available for <code>{contentType}</code> media types.
+        </i>
+      </div>
     }
 
-    return <Input type={"file"} onChange={handleFile} />
+    return <div>
+      { requestBodyDescription &&
+        <Markdown source={requestBodyDescription} />
+      }
+      <Input type={"file"} onChange={handleFile} />
+    </div>
   }