feat (engine): add system stats to the EngineStarted telemetry event (#461)

Description

Add system stats to the EngineStarted telemetry event

• Number CPU
• Total Memory (in bytes)

Total pool size is already collected (pools.total_size)

Related issue

#461

Examples

EngineStarted event

{
  "engine_version": "v3.3.0-23-g08debd6b-20230130-1755",
  "db_engine": "postgres",
  "db_version": "14",
  "pools": {
    "fs_type": "zfs",
    "number": 1,
    "total_size": 167772160,
    "total_used": 135168
  },
  "restore": {
    "mode": "unknown",
    "refreshing": "",
    "jobs": null
  },
  "system": {
    "cpu": 16,
    "total_memory": 14503538688
  }
}

Checklist

• MR description has been reviewed
• MR changes are functionally tested
• MR does NOT have API/CLI changes OR there are API/CLI changes and they have been reviewed & DOCS ARE ADJUSTED (reference doc, etc)
• MR does NOT have UI changes OR there are UI changes and they have been reviewed & UX IS REVIEWED

Closes #461