SPSideBySideSettings: New resource for enabling ZDP with DSC in SP 2016 and 2019

Following up on #1096 about ZDP there would be the need to create a new resource to handle Side-by-Side in this scenario. The new resource could look like this:

Enabling SideBySide could look like this and would set the SideBySide token to the current patch level.

SPZeroDownTimePatching EnableSideBySide {
    SideBySide = “Enable”
}

After the patching is done...
Setting SideBySideToken to the new Farm Version could look like this:

SPZeroDownTimePatching EnableSideBySide {
    SideBySide = “Upgrade”
}

All information needed to set the web application property WebSerivce.SideBySideToken can be obtained within this resource, by querying the farm or using a part of the new methods introduced with the refactoring of SPProductUpdate

Maybe there should be an option available to disable SideBySide - but this is not necessarily a key feature we should implement.

Edit: The resource needs to have a key that can be only two values. This would make it possible to use this resource in a given configuration twice.

Start by reading issue #1096 and the methods introduced by the SPProductUpdate refactoring, since the issue identifies these as sources for the farm version and WebSerivce.SideBySideToken information. Done means a new resource supports the two-value key for enabling and upgrading SideBySide and can be used twice in one configuration; disabling remains optional.