housekeeping: restore start/finish debug logging

Problem: housekeeping debug logs that were recently removed to
reduce noise turned out to be handy when diagnosing #6179.

Restore 2 out of 3 removed debug log messages.

Author: garlick

src/modules/job-manager/housekeeping.c

@@ -317,6 +317,14 @@ static void set_failed_reason (const char **s, const char *reason)
         *s = "multiple failure modes";
 }
 
+static void bulk_start (struct bulk_exec *bulk_exec, void *arg)
+{
+    struct allocation *a = arg;
+    flux_t *h = a->hk->ctx->h;
+
+    flux_log (h, LOG_DEBUG, "housekeeping: %s started", idf58 (a->id));
+}
+
 static void bulk_exit (struct bulk_exec *bulk_exec,
                        void *arg,
                        const struct idset *ids)
@@ -376,7 +384,9 @@ static void bulk_exit (struct bulk_exec *bulk_exec,
 static void bulk_complete (struct bulk_exec *bulk_exec, void *arg)
 {
     struct allocation *a = arg;
+    flux_t *h = a->hk->ctx->h;
 
+    flux_log (h, LOG_DEBUG, "housekeeping: %s complete", idf58 (a->id));
     allocation_remove (a);
 }
 
@@ -830,7 +840,7 @@ struct housekeeping *housekeeping_ctx_create (struct job_manager *ctx)
 }
 
 static struct bulk_exec_ops bulk_ops = {
-    .on_start = NULL,
+    .on_start = bulk_start,
     .on_exit = bulk_exit,
     .on_complete = bulk_complete,
     .on_output = bulk_output,