This changes the behavior of
`matrix_playbook_migration_matrix_nginx_proxy_uninstallation_enabled`
and is against what we initially described in the changelog entry,
but I've discovered some problems when the `matrix-nginx-proxy` service
and container remain running. They need to go.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2999
Related to https://github.com/geerlingguy/ansible-role-docker/pull/410

The newly extracted role also has native Traefik support,
so we no longer need to rely on `matrix-nginx-proxy` for
reverse-proxying to Ntfy.

The new role uses port `80` inside the container (not `8080`, like
before), because that's the default assumption of the officially
published container image. Using a custom port (like `8080`), means the
default healthcheck command (which hardcodes port `80`) doesn't work.
Instead of fiddling to override the healthcheck command, we've decided
to stick to the default port instead. This only affects the
inside-the-container port, not any external ports.

The new role also supports adding the network ranges of the container's
multiple additional networks as "exempt hosts". Previously, only one
network's address range was added to "exempt hosts".