Cloud-init phone home support [maybe]

**Describe the solution you'd like:**
Can we/should we use the cloud-init [phone home module](https://cloudinit.readthedocs.io/en/latest/topics/modules.html#phone-home) to ping an API endpoint to report that a microvm has successfully booted?

This will be problematic with using a macvtap interface because unless the switch supports reflective relay / hairpin mode the microvm and host cannot communicate with each other. But we could add an additional network interface for microvm->host coms

**Why do you want this feature:**
It would be good to understand that a microvm has booted successfully, which includes that cloud-init not erroring.

**Anything else you would like to add:**
Another option could be that we look at the stdout/stderr output instead.

Start by reviewing the cloud-init phone home module and the issue's macvtap networking constraint. Compare reporting through an API endpoint with inspecting stdout/stderr, then define how successful microVM boot and cloud-init completion should be detected and reported.

Written by the indexing model from the issue text.