[FEATURE REQUEST] bootstrap-salt.ps1: needs to handle custom config file in installer

[nosrio]

Description of Issue/Question

Bootstrap script on Windows does not allow to use '/custom-config=' parameter in installer,

Setup

(Please provide relevant configs (Be sure to remove sensitive info).)

Steps to Reproduce Issue

(Include debug logs if possible, bootstrap-salt.sh -D.)

bootstrap-salt.ps1

Versions and Systems

(salt --versions-report, bootstrap-salt.sh -v, system type and version,
cloud/VM provider as appropriate.)

PS C:\Users\60063137> $PSVersionTable


Name                           Value
----                           -----
PSVersion                      5.1.16299.1146
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.16299.1146
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

[nosrio]

I modified the powershell script and added this features. Let me know if i can submit a PR.

[sagetherage]

@nosrio you are welcome to open a PR - I will attempt to get it reviewed in a timely manner, although I have not demonstrated that thus far for this repo, I will try to be better.