[BUG] Add-AutotaskBaseURI Missing Zones

[prismong]

Describe the bug
It's not possible to connect to use this module for the following Autotask zones:

• America East 3 (PHL) - https://webservices22.autotask.net/atservicesrest
• UK 3 (LON) - https://webservices28.autotask.net/atservicesrest

This is because the zones are hard-coded and validated in the Add-AutotaskBaseURI cmd, so it should just need the additional zones added.

To Reproduce
Steps to reproduce the behavior:

1. Use Add-AutotaskBaseURI with a missing zone.
2. The API throws a "Cannot validate argument on parameter 'BaseURI'" error due to the missing zones not being specified in the module.

Expected behavior
Using the Add-AutotaskBaseURI cmd should allow connections to the aforementioned zones.

Current Workaround
I have manually edited the Add-AutotaskBaseURI.ps1 file on my own system to include the additional zones which works as expected.