Add support to a public access to cloudsql-instance (#754)

* feat: add support to a public access to cloudsql-instance

* doc: update cloudsql-instance doc changing the ipv4_enabled parameter description

* test: fix assertion test to ipv4_enabled

modules/cloudsql-instance/variables.tf

@@ -139,3 +139,9 @@ variable "users" {
   type        = map(string)
   default     = null
 }
+
+variable "ipv4_enabled" {
+  description = "Add a public IP address to database instance."
+  type        = bool
+  default     = false
+}