[Messenger] Support SQS Transport with QueueUrl as DSN

**Description**  
The Amazon SQS Transport now only supports a DSN that starts with `sqs://`, 
but especially with CloudFormation the QueueUrl could be provided as an environment variable.

See https://github.com/brefphp/symfony-messenger/pull/30#issuecomment-644228492

**Example** 
```
MESSENGER_TRANSPORT_DSN=https://sqs.us-east-2.amazonaws.com/123456789012/ab1-MyQueue-A2BCDEF3GHI4
```
