Prometheus and grafana port should not be accessible from any address, only myip

[hcoyote]

https://github.com/redpanda-data/openmessaging-benchmark/blob/8411e4a17f9fe190591389bf9b17c515f144a393/driver-redpanda/deploy/provision-redpanda-aws.tf#L176-L188

This should probably be locked down to same address as used for general access to the security group from the tester's home node.

 cidr_blocks = ["${chomp(data.http.myip.body)}/32"]

[hcoyote]

#67 for pr.