Add an option for "UNIX username" and "password" to WSL CLI

Nobody has claimed this yet.

When running
`wsl --install Debian`

User is required to provide username and password:
```
Enter new UNIX username: jr
New password:
Retype new password:
passwd: password updated successfully
Installation successful!
```
I would like to be able to run `wsl --install` in a noninteractive mode (as a part of a script).

**Describe the solution you'd like**
Add sub-options `--install-username` and `--install-password` to `wsl --install` command. The expected usage would be:
`wsl --install Debian --install-username jr --install-password 1234`

**Describe alternatives you've considered**
There are some awkward ways that this can be done in PowerShell e.g. https://superuser.com/questions/1569186/unattended-wsl-ubuntu-18-04-installation-from-powershell, but I don't want to maintain 40 line script for such a simple task.

**Additional context**
I am installing a configuring WSL as a part of an automatic Ansible-like init script here:https://github.com/jan-revay/initPC_Windows (so that every time I get a new machine, I don't have to configure it manually), but as WSL is not capable of being installed in a non-interactive mode - the script stops executing during WSL install (see: ). I would like the script to be fully non-interactive, so I can start it and come to a fully configured machine in 45 minutes.

Review the referenced wsl_install.ps1 and the current `wsl --install` command path; the issue names no repository file or test. Check how noninteractive installation currently handles username and password, with completion meaning the requested options are accepted without prompts and the script-driven install finishes.

Written by the indexing model from the issue text.