ec2: add support for rendering public IP addresses in network config

This bug was originally filed in Launchpad as [LP: #1867197](https://bugs.launchpad.net/cloud-init/+bug/1867197)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2020-03-12T19:14:52.711395+00:00

date_fix_committed = None

date_fix_released = None

id = 1867197

importance = medium

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1867197

milestone = None

owner = chad.smith

owner_name = Chad Smith

private = False

status = triaged

submitter = chad.smith

submitter_name = Chad Smith

tags = []

duplicates = []

_Launchpad user **Chad Smith(chad.smith)** wrote on 2020-03-12T19:14:52.711395+00:00_

cloud-init 20.1 currently renders only local ip address information in the network configuration emitted for attached NICs.

Ec2 instances can be launched and configured with multiple public IP addresses

https://aws.amazon.com/blogs/aws/multiple-ip-addresses-for-ec2-instances-in-a-virtual-private-cloud/

Ec2 IMDS network data exposes public IPv4 addresses in the following metadata keys:
* network.interfaces.macs..public-ipv4s = "18.218.219.181"
* and an association of public ip to the private IPs allocated via the key
"ipv4-associations": {
 "18.218.219.181": "172.31.44.13"
 },

Cloud-init should render known public ipv4 address configuration on the node to avoid network round trips for local services that may connect with the VMs known public IP

No files or tests are named. Start by tracing the EC2 IMDS network metadata for public-ipv4s and ipv4-associations into the network configuration renderer; done when known public IPv4 addresses are emitted for attached NICs without requiring network round trips.

Written by the indexing model from the issue text.