Added Zoomgov.com support

[andrew-hoggins]

Added support for alternate Zoom instances such as Zoomgov.com.
Created parameter "APIConnection" on Connect-PSZoom command where user can specify optional target environment.
Default APIConnection value is set to "zoom.us".
Replaced hardcoded https://api.zoom.us with a variable containing requested site "zoom.us".

# Replaced hardcoded:
"https://api.zoom.us/..."

# Inline Script scope variable
"https://api.$ZoomURI/..."

FYI, first time contributing to a project so if I did something incorrect or not following standards please correct me.

[andrew-hoggins]

Added one additional commit for 3 new commands Add/Remove/Update-zoomphoneusercallingplans. All additional development will wait until pull request has been actioned.

[andrew-hoggins]

Going to do some modifications then resubmit pull request.