[RFE] Add create-user flag to Azure-init CLI

[cadejacobson]

Current situation

Azure-init is aiming to improve its modularity by adding flags for each feature. We would like to be able to create the admin user using one of these flags.

Ideal future situation

We are able to call one of the below flags to have azure-init pull IMDS data, get the user's information, and write it to an available backend.

Implementation options

• azure-init --create-user
• azure-init --create-admin-user

Additional information

This should not be an exclusive flag. We would like the ability to use multiple flags in a call to azure-init (--create-user --configure-sshd)