Update CentOS username on 9+

[jtimberman]

👻 Brief Description

The default username for CentOS (Stream) changed! We should automatically select the right one.

Version

3.19.0

Environment

Nothing special.

Scenario

Specifying the transport user is an additional bit of configuration required for CentOS that isn't required on, e.g., rocky or ubuntu.

Steps to Reproduce

Add centos-9 or centos-10 to a kitchen.yml without specifying the transport.username results in being unable to SSH.

Expected Result

SSH succeeds.

Actual Result

SSH times out.

➕ Additional context

I'll have a pull request shortly!