feat: Add has-changes output to expose plan change detection

[jamengual]

Summary

• Adds a new has-changes output that exposes whether the Terraform plan contains infrastructure changes
• The output is a string value of "true" or "false"

Motivation

Currently, consumers who want to conditionally run steps based on whether the plan has changes must parse the summary output. The action already computes this internally (used for Infracost integration), but doesn't expose it.

This change simply exposes the existing steps.atmos-plan.outputs.changes value as a proper action output.

Usage

- uses: cloudposse/github-action-atmos-terraform-plan@v4
  id: plan
  with:
    component: mycomponent
    stack: dev

- if: steps.plan.outputs.has-changes == 'true'
  run: echo "Infrastructure changes detected"

Test plan

• Verify output is "true" when plan has changes
• Verify output is "false" when plan has no changes

[github-actions]

Changes Found for foobar/changes in plat-ue2-sandbox

Plan: 1 to add, 0 to change, 0 to destroy.

To reproduce this locally, run:

atmos terraform plan foobar/changes -s plat-ue2-sandbox

---

Create

+ random_id.foo[0]

Terraform Plan Summary

  # random_id.foo[0] will be created
  + resource "random_id" "foo" {
      + b64_std     = (known after apply)
      + b64_url     = (known after apply)
      + byte_length = 8
      + dec         = (known after apply)
      + hex         = (known after apply)
      + id          = (known after apply)
      + keepers     = {
          + "seed" = "foo-plat-ue2-sandbox-blue"
        }
    }

Plan: 1 to add, 0 to change, 0 to destroy.

Warning: Test warning summary

  with data.validation_warning.warn[0],
  on main.tf line 20, in data "validation_warning" "warn":
  20: data "validation_warning" "warn" {

Test warning details

Warning

Warning: Test warning summary

  with data.validation_warning.warn[0],
  on main.tf line 20, in data "validation_warning" "warn":
  20: data "validation_warning" "warn" {

Test warning details

[github-actions]

These changes were released in v5.7.1.