Add reusable storage pool module with lvmcluster san pool

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

incus/modules/storage/variables.tf

@@ -0,0 +1,25 @@
+variable "name" {
+  type = string
+}
+
+variable "driver" {
+  type = string
+}
+
+variable "hypervisors" {
+  type = set(string)
+}
+
+variable "witnesses" {
+  type = set(string)
+}
+
+variable "hypervisor_config" {
+  type    = map(string)
+  default = {}
+}
+
+variable "witness_config" {
+  type    = map(string)
+  default = {}
+}