fix: use new name of illustration (#4093)

Author: Slashgear

managed-databases/mongodb/index.mdx

@@ -9,7 +9,7 @@ content:
 
 <ProductHeader
    productName="Managed MongoDB® Databases"
-   productLogo="documentDB"
+   productLogo="mongoDB"
    description="Managed MongoDB® Databases provide fully-managed databases with a MongoDB® compatible API, relying on MongoDB® and PostgreSQL as storage engines. Enjoy automatic backups, scaling, monitoring and much more."
    url="/managed-databases/mongodb/quickstart/"
    label="Managed MongoDB® Databases Quickstart"