[Build] Create child builds (#7941)

* Add "create_child_builds" field to BuildOrder serializer

- only when creating a new order
- write only field

* Update serializer field

* Add placeholder task for creating child build orders

* Add field to PUI forms

* Auto-create build orders as required

* Bump API vresion

* Add documentation

* Update unit tests

src/frontend/src/forms/BuildForms.tsx

@@ -47,7 +47,7 @@ export function useBuildOrderFields({
   const globalSettings = useGlobalSettingsState();
 
   return useMemo(() => {
-    return {
+    let fields: ApiFormFieldSet = {
       reference: {},
       part: {
         disabled: !create,
@@ -119,6 +119,12 @@ export function useBuildOrderFields({
         }
       }
     };
+
+    if (create) {
+      fields.create_child_builds = {};
+    }
+
+    return fields;
   }, [create, destination, batchCode, globalSettings]);
 }