support custom url for FedRamp customers in the servicenow integration

[Ibrahim-Abu-Rmaileh]

As part of fixing SLK-110845: Unable to Use Custom URL for SNOW Integration

I made the changes to support custom URL. This way we don’t have to constrcut the Instance URL at the backend by binding the baseServer to the Instance Name, when we we’re not really sure what should be the baseServer.
This way the user him self provide the full final URL of his instance and we use it directly instead of trying to construct it and potentially crash.

The motivation behind this is to start supporting Fedramp customers that have a server different from the base server (service-now.com).

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