Support for alternate credentials in Start-ChocolateyProcessAsAdmin

**What you are Seeing?**
Certain custom installers will perform operations/requests to other applications across the network. For example, and application that inside of it's setup.exe, want's to confirm access to a relational database.
In some scenarios, choco is being called or executed via software orchestration tool like Puppet / Octopus Deploy / other.
Their service might be a virtual a/c (NT Service\serviceName) or a system a/c (Local Service).
Those a/c's won't have access to the network resource.

**Desired Functionality**
Because the Start-ChocolateyProcessAsAdmin.ps1 is in the background spawning a [System.Diagnostics.Process], that supports providing alternate user credentials to spawn the process as. Now, of course there's ensuring that the service a/c has the privileges to impersonate a user, and also run in a non-interactive session that will require some work with Win32API's.
However, this is quite often a requirement for packages that organizations build for distributing some of their enterprise software.

Start with Start-ChocolateyProcessAsAdmin.ps1 and its use of System.Diagnostics.Process. Investigate the stated Win32 API requirements for alternate credentials, impersonation privileges, and non-interactive sessions; done means service accounts can launch custom installers with alternate credentials for network access.

Written by the indexing model from the issue text.