feat: implement RFC 16 to allow emergency node access

[miampf]

Context

This PR aims to implement RFC 16: Node access.

Proposed change(s)

This PR only implements part of the RFC. Currently, the following is implemented:

• The openssh-server package was added to the node image
• OpenSSH was configured to only allow public key authentication and use a CA public key as a user certificate
  • The derivation of this certificate will be handled in another PR.
• A new terraform variable emergency_ssh was added to allow control over load balancing ports. Currently, this is implemented (and tested) for
  • azure
  • aws
  • gcp
  • openstack
• The emergency ssh e2e tests on this PR don't work since they reference the latest debug image build from main, which does not include the SSH server. The "all at once" test under additional information uses the same workflow, but with an image built from this branch.

Additional info

• working E2E tests:
  • azure
  • aws
  • gcp
  • all at once (e2e-ssh workflow)

Checklist

• Run the E2E tests that are relevant to this PR's changes
• Update docs
• Add labels (e.g., for changelog category)
• Is PR title adequate for changelog?

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Coverage report

Package	Old	New	Trend
cli/internal/cmd	57.90%	57.90%	↔️