chore(docker): the history move logs which services its old keys belong to (#6718)

#6718 "A swarm container's metrics, normal and anomalies are keyed by its task
name, so they start over whenever the task moves". The move found 391,091
hourly-only task names against 51 services and about 400 keys with raw samples.
Log the services with the most keys and a few names, to read before those keys
start moving.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/docker/rekey.py

@@ -13,6 +13,7 @@ from __future__ import annotations
 import asyncio
 import logging
 import time
+from collections import Counter
 from typing import TYPE_CHECKING
 
 from sqlalchemy import delete, select, text, update
@@ -90,6 +91,9 @@ async def old_keys(session) -> list[str]:
              | await names(MaintenanceWindow.scope_resource, MaintenanceWindow.scope_source == "docker"))
     logger.info("Swarm history under task names: %d keys with raw samples, %d with hourly rows, "
                 "%d named by anomalies, rules or windows", len(recent), len(hourly), len(named))
+    by_service = Counter(task_service(k.split("/", 1)[1]) for k in hourly - recent)
+    logger.info("Swarm history under task names, hourly only, most keys first: %s; for example %s",
+                by_service.most_common(10), sorted(hourly - recent)[:3])
     return sorted(hourly - recent) + sorted((named - hourly) - recent) + sorted(recent)