(Optional) Retrieve the public key of the Unwired Server to populate its value in the provisioning file.
During startup, the server verification key is stored in a text file called ServerVerificationKey.txt in <UnwiredPlatform_InstallDir>/Servers/MessagingServer. It is created only at messaging service startup, so the messaging service must be started at least once to see this file. The data in this file is the Base64 encoded server verification key and should be used as the value for the serververificationkey= key.