fix: webhook validation with an array parameter

[askel4dd]

Fixes

Conversations API onConversationAdd webhook MessagingBinding.Address parameter can be either string or array<string> (you can see it underneath the parameters table in the Note section). twilio-node library will always fail to validate such webhooks because array parameters are not supported. In this pull-request I added a support for such parameters, but nothing more than that — deeply nested arrays, or object parameters are still not supported and I am not sure If they should be.

Checklist

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