Make "data-dir" allowed for ETCD

[SoulKyu]

Hello !

Just wanna open a discussion on etcd and the facts that its storage location is currently only on the EPHEMERAL storage of Talos nodes.

Would it be possible to make it available on the user storage space ? What is the current blocking aspect of Talos that does not allow configuration of a custom data-dir ? maybe maintenance tasks ?

I've a setup like this in mind:

cluster:
  etcd:
    extraArgs:
        listen-metrics-urls: http://0.0.0.0:2381
        data-dir: /var/mnt/etcd-data
---
apiVersion: v1alpha1
kind: UserVolumeConfig
name: etcd-data
provisioning:
  diskSelector:
    match: "!system_disk"
  minSize: 15GB
  maxSize: 15GB

Thanks you !

[smira]

This is #10678