fix(mdb): public beta message (#4373)

Author: ldecarvalho-doc

pages/managed-mongodb-databases/index.mdx

@@ -16,7 +16,7 @@ content:
 />
 
 <Message type="important">
-Managed MongoDB® is currently in private beta. Click [here](https://www.scaleway.com/en/managed-mongodb/) to join the waiting list.
+Managed MongoDB® is currently in public beta. [Fill out the form](https://www.scaleway.com/en/managed-mongodb-form/) to be notified of the General Availability or if you want to get in touch with our team about Managed MongoDB®.
 </Message>
 
 ## Getting Started