Align metric names with Prometheus naming conventions

Use base units, export cumulative values as _total counters, update docs, dashboards and rules.

metrics/pve_node_subscription_collector.go

@@ -49,8 +49,8 @@ func NewPveSubscriptionCollector(apiClient *proxmox.PveApiClient, registry *TTLR
 	// Node subscription registration date.
 	c.regDate = NewTTLGaugeVec(
 		prometheus.GaugeOpts{
-			Name: "pve_node_subscription_regdate",
-			Help: "Node subscription registration date.",
+			Name: "pve_node_subscription_registration_timestamp_seconds",
+			Help: "Node subscription registration date as a unix timestamp in seconds.",
 		},
 		[]string{"cluster", "node"},
 		5*time.Minute,
@@ -60,8 +60,8 @@ func NewPveSubscriptionCollector(apiClient *proxmox.PveApiClient, registry *TTLR
 	// Node subscription next due date.
 	c.nextDueDate = NewTTLGaugeVec(
 		prometheus.GaugeOpts{
-			Name: "pve_node_subscription_nextduedate",
-			Help: "Node subscription next due date.",
+			Name: "pve_node_subscription_next_due_timestamp_seconds",
+			Help: "Node subscription next due date as a unix timestamp in seconds.",
 		},
 		[]string{"cluster", "node"},
 		5*time.Minute,