[docs]: Development documentation: How to test code changes in my local cloud-init repo when spinning up a new VM?

# Documentation request

Hi, I have started working on a bug (my first) in cloud-init but I want to understand how I can manually check that my code is working.

I have went through the documentation and couldn't find anything about local deployment. The closest I found was the how to [test the pre-release cloud-init](https://docs.cloud-init.io/en/latest/howto/ubuntu_test_prerelease.html) tutorial.

My guess is to build the python wheel out of the source code then installing it on the VM.

The other part of my question is how to test my local package on the first boot of the VM (which is the intended use case of `cloud-init`) and not via `sudo cloud-init clean --logs --reboot` (which is more of a workaround). Is it some `virt-customize` magic on the cloud image before running the VM?

If someone couldjust share their script in this issue without necessarily working on updating the documentation, that would be great as well to unblock me. Thanks!