Introduced a new `AddReceiver` method in the `Extension` class to facilitate adding a receiver to an envelope. This method includes parameters for `envelope_uuid`, `emailAdress`, `salutation`, and an optional `phone`, along with XML documentation for clarity.
Removed the `EnvelopeReceiverCreateReadSQL` class and added the `EnvelopeReceiverAddReadSQL` class, which defines the SQL command for adding a receiver. The new class also includes XML documentation comments for better understanding.
