admin api: implement PreviewClusterLayoutChanges

src/api/admin/openapi.rs

@@ -117,6 +117,21 @@ Contrary to the CLI that may update only a subset of the fields capacity, zone a
 )]
 fn UpdateClusterLayout() -> () {}
 
+#[utoipa::path(post,
+    path = "/v2/PreviewClusterLayoutChanges",
+    tag = "Cluster layout",
+    description = "
+Computes a new layout taking into account the staged parameters, and returns it with detailed statistics. The new layout is not applied in the cluster.
+
+*Note: do not try to parse the `message` field of the response, it is given as an array of string specifically because its format is not stable.*
+    ",
+	responses(
+            (status = 200, description = "Information about the new layout", body = PreviewClusterLayoutChangesResponse),
+            (status = 500, description = "Internal server error")
+        ),
+)]
+fn PreviewClusterLayoutChanges() -> () {}
+
 #[utoipa::path(post,
     path = "/v2/ApplyClusterLayout",
     tag = "Cluster layout",
@@ -686,6 +701,7 @@ impl Modify for SecurityAddon {
         // Layout operations
         GetClusterLayout,
         UpdateClusterLayout,
+        PreviewClusterLayoutChanges,
         ApplyClusterLayout,
         RevertClusterLayout,
         // Key operations