k3d dev script improvements

Allow the "-m" for metal-lb to optionally use the public or the private IP for the k3d cluster. Previously the metal-lb option defalted to private IP with no option to use public IP.

Usage Examples:

1. For metal-lb with private IP
   k3d-dev.sh -m -p
2. For metal-lb defaulting to use the public IP
   k3d-dev.sh -m