Added initial, aka seed, value (-InitValue) parameter to Reduce-Object

[SlavaKozlov]

Per suggestion on Medium, I added an initial (or seed) value parameter to the Reduce-Object function (parameter name is -InitValue).

This is useful in multiple piping steps to avoid having to find a way to insert the inti value midstream.

Instead of this:
$values = Step1 | Step2 | Step3
$result = @($init) + $values | Reduce-Object $accumulator

We can do this:
$result = Step1 | Step2 | Step3 | Reduce-Object $accumulator -InitValue $init

Added unit test as well.
Thx