demo: Activate PostgreSQL slow logs

This commit will cause PostgreSQL to log any database statements taking
longer than 500 ms. This is useful to flag any slow queries running in
Praefect.

_support/terraform/terraform/main.tf

@@ -47,6 +47,11 @@ resource "google_sql_database_instance" "praefect_sql" {
   settings {
     tier = "db-f1-micro"
 
+    database_flags {
+      name  = "log_min_duration_statement"
+      value = "500"
+    }
+
     ip_configuration{
       ipv4_enabled = true