[ISSUE] Add mutex for creating storage mounting cluster

[nfx]

Mounting array of resources creates dedicated automated cluster, though it should not:

resource "databricks_azure_blob_mount" "this" {
  for_each             = toset(var.categories)
  container_name       = "insights-logs-${each.value}"
  storage_account_name = azurerm_storage_account.this.name
  mount_name           = "audit-${each.value}"
  auth_type            = "ACCESS_KEY"
  token_secret_scope   = databricks_secret_scope.mounts.name
  token_secret_key     = databricks_secret.storage_key.key
}