More improvements to backend deploy action

[jkatofsky]

• Fail the whole action on any command
• Use Node 20
• Install with frozen lockfile (best practice)
• Keep the yarn cache cleaned to keep more storage free
• Use pm2 restart instead of a delete/start. This is better because:
  • no downtime while are we rebuilding the app
  • we only restart the app once the deploy has succeeded

[netlify]

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