Update Terraform configuration to add user data

During initialization, a test script is run. Update workflow.

.github/workflows/benchrunner-aws.yml

@@ -1,7 +1,10 @@
 name: Deploy benchrunner to AWS
 
 on:
-  [push]
+  push:
+    branches:
+      - main
+  workflow_dispatch: {}
 
 jobs:
   deploy:

terraform/init.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+echo "This is a test file was created during the instance initialization." > test.txt

terraform/main.tf

@@ -85,6 +85,7 @@ resource "aws_instance" "bench_runner" {
   key_name               = "bench-runner"
   vpc_security_group_ids = ["${aws_security_group.ingress_all.id}"]
   subnet_id              = aws_subnet.subnet1.id
+  user_data              = file("init.sh")
 
   tags = {
     Name = "BenchmarkingEC2Runner"