Allow to override remote user in machine init

[arixmkii]

Is this a BUG REPORT or FEATURE REQUEST? (leave only one on its own line)

/kind feature

Description

It is allowed to provide custom image during init https://github.com/containers/podman/blob/main/cmd/podman/machine/init.go#L92 and it is supported, but there is no way to provide remote user in the same time and one will need to edit config manually afterwards. Introducing this parameter will grant more options for custom images.

This will become valuable, when multiple providers are supported for a single target (Qemu + vfkit for Apple Macs or Qemu + WSL + Hyper-V for Windows hosts). Discovered during experiment with #13006

Steps to reproduce the issue:

1. run podman machine init

Describe the results you received:

No way to change remote user during the init command.

Describe the results you expected:

--remote-user myuser would be supported. Name of the key could be different to match all the scenarios better.

Additional information you deem important (e.g. issue happens only occasionally):

Output of podman version:

Client:       Podman Engine
Version:      4.2.0
API Version:  4.2.0
Go Version:   go1.18.5
Built:        Wed Aug 10 23:46:05 2022
OS/Arch:      darwin/arm64

Server:       Podman Engine
Version:      4.1.1
API Version:  4.1.1
Go Version:   go1.18.4
Built:        Fri Jul 22 22:06:49 2022
OS/Arch:      linux/arm64

Have you tested with the latest version of Podman and have you checked the Podman Troubleshooting Guide? (https://github.com/containers/podman/blob/main/troubleshooting.md)

Yes (built from source)

Additional environment details (AWS, VirtualBox, physical, etc.):

Podman machine on Mac and Windows hosts.