Kafka Default SSH Tunnel

[dehume]

Fixes #357

Allow users to set a default ssh connections for brokers in Kafka connections. Currently ssh_tunnel is a top level attribute for Kafka connections so only a single ssh connection can be applied to all brokers. Adding ssh_tunnel as an attribute within the broker block (the same way aws privatelink is handled):

resource "materialize_connection_kafka" "kafka_connection" {
  kafka_broker {
      broker = "broker:9092"
      ssh_tunnel {
          name = materialize_connection_ssh_tunnel.tunnel.name
    }
  }
}

Will apply the ssh connection to that broker:

CREATE CONNECTION kafka_connection TO KAFKA (
    BROKERS ('broker1:9092' USING SSH TUNNEL ssh_connection)
);

And setting the ssh_tunnel at as a top level attribute will set the default:

resource "materialize_connection_kafka" "kafka_connection" {
  ssh_tunnel {
      name = materialize_connection_ssh_tunnel.tunnel.name
  }
  kafka_broker {
      broker = "broker:9092"
  }
}

CREATE CONNECTION kafka_connection TO KAFKA (
    BROKERS ('broker1:9092'),
    SSH TUNNEL ssh_connection
);