Avoid syncing buckets with invalid secrets

[sancyx]

As Pipeline tries to sync content of these buckets automatically every 20 minutes or when backupbuckets/sync is called via API there could be several errors logged like secretId doesn't exists anymore or is invalid.
Even if all backups are deleted from bucket, or bucket doesn't exists anymore we will try to fetch backups until the bucket is deleted from Pipeline DB however currently there's no possibility to list/delete backup buckets on UI or using CLI only via API.
We should solve this problem either with an automatic garbage collection or make possible to list/delete buckets via UI/CLI.