desktop live installer: cloud-init/ubuntu-desktop-installer network config naming collisions

Seen on live desktop isos build date:
$ cat /cdrom/.disk/info
Ubuntu 23.04 "Lunar Lobster" - Dail amd64 (20230407)
$ snap list ubuntu-desktop-installer
Name Version Rev Tracking Publisher Notes
ubuntu-desktop-installer 0+git.f46d534e 922 latest/stable/… canonical✓ classic

Desktop live installer prefers NetworkManager backend for network config due to a netplan config file /etc/netplan/01-network-manager.yaml which contains:

network:
  version: 2
  renderer: NetworkManager

livecd-rootfs configures cloud-init to write directly to /etc/NetworkManager/system-connections when discovering network due to a config snippet at
/etc/cloud/cloud.cfg.d/99-installer-use-networkmanager.cfg which sets cloud-init to write directly to /etc/NetworkManager/system-connections with this config:
# Automatically generated by installer build process
system_info:
  network:
    renderers: ['network-manager']
    activators: ['network-manager']

-
This tells cloud-init to write out /etc/NetworkManager/system-connections/cloud-init-enp1s0.nmconnection directly.

Later Ubuntu-desktop-installer(subiquity) starts, it may set network config and write it to /etc/netplan/00-installer.yaml and trigger a 'netplan apply'.

If there is a non-empty netplan config at this time, subiquity writes out /etc/netplan/00-installer.yaml and renames any other existing netplan yaml files to /etc/netplan/*.yaml.dist-subiquity.

Then subiquity(ubuntu-desktop-installer) invokes netplan apply to render all applicable network config to the ephemeral (installer) environment.

When netplan is rendering to `backend: NetworkManager` instead of the default networkd and it'll write /etc/NetworkManager/netplan-*.nmconnection files with connection names scoped under `netplan-`. Cloud-init's rendered connections are scoped under `cloudinit-`. This results in a split brain problem where cloudinit's configuration and netplan's configuration are not aware of each other and netplan isn't aware of any pre-existing /etc/NetworkManager artifacts. We then have conflicting nm connections being defined and named for the same underlying network interfaces. This results in inability to run: nmcli load /etc/NetworkManager/system-connections/cloud-init-enp1s0.nmconnection with errors such as "unknown connection" or "ipv4.gateway: gateway cannot be set if there are no addresses configured"

Ideally we probably want both cloud-init and subiquity to be configuring network in netplan config files so that any merged network config is well known by netplan and results in a single source of truth for network config.

This may mean dropping the overrides provided by livecd-roots setting cloud-init to render directly to network-manager.