Add user and group support for Windows systems

[gravesb]

As a Splunk Maintainer,
I want to configure ownership of Splunk on Windows,
So that I can increase security of the Splunk installation

We'll know we're done when:

• Owner and group can be specified for a Windows Splunk installation
• A virtual account can be used as the Splunk user

Additional notes:
A password will be required for non-virtual accounts (regular users and Managed Service Accounts). Specifically, the password is necessary to run the Splunk service. It is not necessary at installation time (except for MSI installs).

It may be desirable to set up virtual accounts before the first time run (or in the case of an msi install, disable the service, set up the account, and re-enable it) given the difficulties of managing virtual accounts with the different install methods and the fact that the service/virtual account will not exist until the first time run.