Configure and test SAP OData v4 service on SAP Gateway with $filter, $expand, and deep insert

Steps

1. Register the OData v4 service in the SAP Gateway server via transaction /IWFND/V4_ADMIN and activate it; verify accessibility via the service document URL /sap/opu/odata4/<namespace>/<service>/<binding>/
2. Test $filter expressions against the entity set: string filters use single quotes and the 'eq', 'ne', 'gt', 'lt', 'contains', 'startswith' functions; date literals use the format YYYY-MM-DDThh:mm:ssZ
3. Use $expand with navigation properties to retrieve related entities in a single request; in OData v4 $expand supports nested $select, $filter, and $orderby within the expanded navigation
4. For deep insert (creating a parent entity and its related entities in one POST), include the navigation property data as a nested object in the POST body under the navigation property name
5. Validate that the ABAP backend implements the necessary CREATE_DEEP_ENTITY method in the data provider class for deep insert; absence of this implementation returns a 405 Method Not Allowed