Adds support for additional security groups (#4)

* Added support for attaching additional security groups to the EC2 instance

* Performed terraform fmt

* Restored sample

ec2.tf

@@ -55,7 +55,10 @@ resource "aws_launch_template" "main" {
     description                 = "${var.name} ephemeral public ENI"
     subnet_id                   = var.subnet_id
     associate_public_ip_address = true
-    security_groups             = [aws_security_group.main.id]
+    security_groups = concat(
+      [aws_security_group.main.id],
+      var.additional_security_group_ids
+    )
   }
 
   dynamic "instance_market_options" {

variables.tf

@@ -115,4 +115,10 @@ variable "tags" {
   description = "Tags to apply to resources created within the module"
   type        = map(string)
   default     = {}
+}
+
+variable "additional_security_group_ids" {
+  description = "A list of identifiers of security groups to be added to the EC2 instance"
+  type        = list(string)
+  default     = []
 }