Feature/db snapshots

[Yiakman]

No description provided.

[acedward]

• Add comment / docs on how to use the backup
• Make the retention policy smarter, as backups are stored in the HD
  • Last day per hour
  • Last 3 days each 6 hours
  • Last N days one per day
• Default values for the setup, ideally 0 config to make it work.
• Some comment explaining the data[0] === 0x51 && dataStr.includes("PAIMA_SNAPSHOT_TRIGGER") to intercept this message
• Not sure this will work for real pgsql database as this is implemented in the start pglite

[Yiakman]

replaced by #669