Provisions the substrate for the kube-proxmox Flux cluster on london-a:
a control-plane VM (k3s installed later by the k3s_server Ansible role) and
a worker template that kproximate clones to autoscale. Wires a bpg/proxmox
provider (api token + SSH to root@london-a for snippet upload) into the root
module. Workers auto-join k3s via a cloud-init snippet; the join token is a
two-phase apply (see proxmox/README.md).
* Grafana Cloud migration, adding dashboards, fleet, alloy and synthetics
* modulize stuff now that we have multiple substantial things in here
* provider updates and new secrets
* remove grafana and prometheus from ansible
