Check connection acknowledgement for all messages, not just trust ping and ack

[TimoGlastra]

Currently when receiving a trust ping or ack message we check whether the connection state is not yet completed. If this is the case we set the connection state to Complete.

However per the connection RFC on connection acknowledgement: "As any message will confirm the connection, any message will do."

So we need to move this implementation to a place where it will be run for every incoming message. I think the best way would be to allow for agent middleware, see #97 . After this is implemented we could address this issue.

// TODO: This is better addressed in a middleware of some kind because
// any message can transition the state to complete, not just an ack or trust ping
if (connection.state == ConnectionState.Responded && connection.role === ConnectionRole.Inviter) {
  await this.connectionService.updateState(connection, ConnectionState.Complete);
}