feat: Remove sandbox account

[DafyddLlyr]

What does this PR do?

• Retires the PlanX "sandbox" infrastructure stack

Steps taken

• pulumi destroy --stack sandbox on all layers (application, data, networking, certificates)
  • This removed most resources, but not all frustratingly. This means there will likely still be a small bill for the next 90 days.
• pulumi stack rm sandbox on all layers
• Close AWS account (this gets "suspended" for 90 days and is then closed)
• Remove any DNS records on Cloudflare
• Remove references to "sandbox" in codebase

To test / verify

• Pulumi dashboard no longer lists "sandbox" stack
• AWS account shows as suspended when you attempt to log in
• Unable to access Sandbox credentials via AWS SSO

[github-actions]

Removed vultr server and associated DNS entries

[Mike-Heneghan]

Looking good to me 👍

I had a wee look on Cloudflare and it seems like planx.in is still active but I thought that was the one associated with the sandbox?

I might be getting the wrong end of the stick and I think it's non-blocking regardless.

[DafyddLlyr]

That's correct - the domain is still ours and registered in CloudFlare (I'll raise with Helen & Alastair), but all DNS records and Zero Trust rules have been removed.