feat: add proxmox_node_status data source

[cgoolsby]

Summary

• Adds a new proxmox_node_status data source that queries the Proxmox /nodes API endpoint
• Exposes whether a node is in HA maintenance mode via the maintenance boolean attribute
• Also surfaces status, uptime, cpu, mem_used, and mem_total for convenience

Motivation

The primary use case is excluding nodes in maintenance mode from workload placement. Without this data source, there is no way to query node-level status from within Terraform, leaving users no option but to manually check the Proxmox UI before running terraform apply.

Usage

Prevent deploying onto a node in maintenance mode:

data "proxmox_node_status" "pve1" {
  node = "pve1"
}

resource "proxmox_vm_qemu" "app" {
  target_node = "pve1"

  lifecycle {
    precondition {
      condition     = !data.proxmox_node_status.pve1.maintenance
      error_message = "Node pve1 is in maintenance mode — refusing to deploy."
    }
  }
}

Skip resources on a maintenance node:

resource "proxmox_vm_qemu" "app" {
  count       = data.proxmox_node_status.pve1.maintenance ? 0 : 1
  target_node = "pve1"
}

Notes

• No changes to proxmox-api-go required — uses the existing GetNodeList() method
• The maintenance field is absent from the API response for normal nodes and safely defaults to false; Proxmox sends a numeric 1 when the HA manager places a node into maintenance mode
• maintenance and status are kept as separate attributes because they are orthogonal: a node can be online and in maintenance simultaneously

Test plan

• go build ./... passes
• go vet ./... passes
• staticcheck ./... passes
• go test -race -vet=off ./... passes
• Verify maintenance = true when node is in maintenance mode in Proxmox web UI
• Verify maintenance = false for a normal online node