Add resource_category as serializer field that is displayed in the /learning_resource, /learning_resource_search results
Add resource_category as a facet for aggregations and filtering on the /learning_resource_search api and filter on the /learning_resource api
Remove is_learning_material as a filter and aggregation option. It is useful to keep it as a field in the index (that is not displayed in the results) for the upcoming sort. Change the calculation for is_learning_material to use resource_category