* provider/aws: Add aws_alb_listener data source
This adds the aws_alb_listener data source to get information on an AWS
Application Load Balancer listener.
The schema is slightly modified (only option-wise, attributes are the
same) and we use the aws_alb_listener resource read function to get the
data.
Note that the HTTPS test here may fail due until
hashicorp/terraform#10180 is merged.
* provider/aws: Add aws_alb_listener data source docs
Now documented.