Add an option to VpcArgs to allow the user to specify exact AZs

[pgavlin]

i.e. rather than just specifying a count, allow the user to specify [ "us-east-1b", "us-east-1c" ] or similar.

[CyrusNajmabadi]

This is supported in the new Vpc abstraction. When you define your VpcSubnetLocation you can specify either an availabilityZone or an availableZoneId. i.e.

new Vpc("name", {
  subnets: [{
    type: "public",
    location: {
      availabilityZone: "us-east-1b",
      cidrBlock: ...
    }],
});

[CyrusNajmabadi]

I updated this to no longer reference 'Network'. 'Network' is deprecated and will be removed from 1.0