(#22368) allow agent environment

This allows agent environment to be set during the installer and adds
environment=ENV to the puppet.conf file. By default when
environment is left blank in the installer, it will be set to production.

This brings parity of this feature to Windows as compared with non-Windows OSes (they already have
the ability to specify agent environment during installation).

You can set this in the installer or pass it as a MSI property PUPPET_AGENT_ENVIRONMENT.