optimize backup schedules: compress dumps, stagger to weekly, extend retention

- dbaas: gzip MySQL/PostgreSQL dumps, stagger to 0:30, clean old uncompressed
- infra-maintenance: etcd backup daily→weekly Sunday 1am
- redis: backup hourly→weekly Sunday 3am, retention 7→28 days
- vault: raft backup daily→weekly Sunday 2am

stacks/infra-maintenance/modules/infra-maintenance/main.tf

@@ -81,7 +81,7 @@ resource "kubernetes_cron_job_v1" "backup-etcd" {
     namespace = "default"
   }
   spec {
-    schedule                      = "0 0 * * *"
+    schedule                      = "0 1 * * 0"
     successful_jobs_history_limit = 1
     failed_jobs_history_limit     = 1
     concurrency_policy            = "Forbid"