fix: move expires_at to Optional section in docs

Author: jremy42

docs/actions/mongodb_instance_snapshot_action.md

@@ -10,11 +10,11 @@ page_title: "Scaleway: scaleway_mongodb_instance_snapshot_action"
 
 ### Required
 
-- `expires_at` (String) Expiration date of the snapshot in RFC3339 format (ISO 8601).
 - `instance_id` (String) MongoDB instance ID to snapshot. Can be a plain UUID or a regional ID.
 
 ### Optional
 
+- `expires_at` (String) Expiration date of the snapshot in RFC3339 format (ISO 8601). If not set, the snapshot will not expire.
 - `name` (String) Name of the snapshot. If not set, a name will be generated.
 - `region` (String) Region of the MongoDB instance. If not set, the region is derived from the instance_id when possible or from the provider configuration.
 - `wait` (Boolean) Wait for the snapshot to reach a terminal state before returning.