private static String toString(Reindexing.State state) {
        return switch (state) {
            case READY -> "pending";
            case RUNNING -> "running";
            case SUCCESSFUL -> "successful";
            case FAILED -> "failed";
        };
    }
Allows inspecting reindexing status over HTTP.

@author jonmv
clustercontroller-reindexer/src/main/java/ai/vespa/reindexing/http/ReindexingV1ApiHandler.java