feat(container): secure Docker login int-feat-containers (scaleway#3999)

Author: ahamez

containers/container-registry/quickstart.mdx

@@ -47,11 +47,11 @@ Scaleway [Container Registry](/containers/container-registry/concepts/#container
 3. Copy the push instructions. Then click **X** to close the pop-up.
 4. Open a terminal window on your local computer. Then log into the namespace by running the following command from the terminal:
     ```
-    docker login rg.fr-par.scw.cloud/mynamespace -u nologin -p [SCW_SECRET_KEY]
+    echo <SCW_SECRET_KEY> | docker login rg.fr-par.scw.cloud/<NAMESPACE> -u nologin --password-stdin
     ```
 
     <Message type="important">
-      Replace `[SCW_SECRET_KEY]` with your [API secret key](/identity-and-access-management/iam/how-to/create-api-keys/) and `mynamespace` with the name of your namespace.
+      Replace `<SCW_SECRET_KEY>` with your [API secret key](/identity-and-access-management/iam/how-to/create-api-keys/) and `<NAMESPACE>` with the name of your namespace.
     </Message>
 
     Once logged in, a confirmation is displayed:
@@ -96,4 +96,4 @@ You are now logged in and ready to push and pull images to and from your Contain
 
 <Message type="note">
   The current configuration allows you up to 20 pulls/min per image.
-</Message>
+</Message>