Version 5.0.3 - Add RegistrationToken support (and 5.0.2)

[willrutherford]

Add CustomerID (via @Robby-Swartenbroekx v5.0.2) and RegistrationToken support for 2020.1 agent compatibility.

[prejay]

The changes look fine to me, but I think this should be forked off since 2020.x no longer supports installs of new devices running legacy OS agents eg XP, Vista, 2003, 2008, 2008R2 since those older agents don't have any awareness of the now mandatory Registration Token.
Installation of a 2020.x agent may work with, but I won't take responsibility of any issues encountered afterwards as the device willl now be unsupported by Microsoft and Solarwinds.
The safer option is for the deployment package to abort if legacy OS is detected and the user can perform a manual install at their own risk.

Personally I would also prefer a function within the install script to pull through the registration token for the given Customer ID which is easy to do, but would require authentication to the N-Central Server which means providing credentials which some many not like.
The responsible alternative would be to provide a script/AMP that can be run from N-Central as a service that updates the values within the PartnerConfig.xml.
This would also require api interaction since SolarWinds have provided no native method to obtain registration tokens.