dev: limit dev previewer and ignore SSH key files

dev/.gitignore

@@ -0,0 +1,2 @@
+bastion_rsa
+bastion_rsa.pub

dev/constellations-previewer.tf

@@ -42,6 +42,7 @@ resource "azurerm_linux_web_app" "cx_previewer" {
   service_plan_id     = azurerm_service_plan.cx_previewer.id
 
   app_settings = {
+    "CONSTELLATIONS_MAX_THREADS"      = "2"
     "MONGO_CONNECTION_STRING"         = azurerm_cosmosdb_account.cx_backend.connection_strings[0]
     "AZURE_STORAGE_CONNECTION_STRING" = azurerm_storage_account.constellations.primary_connection_string
     "NUXT_PUBLIC_API_URL"             = "https://api.${var.tld}"