feature: Add auto_confirm_sns_subscription flag for civiform_alert_subscription

[osajulian-dev]

Description

This PR adds a new auto_confirm_sns_subscription flag to conditionally auto-confirm SNS email subscriptions using the endpoint_auto_confirms attribute in Terraform.

Specifically:

• Adds a new auto_confirm_sns_subscription boolean variable (default: false)
• Applies this flag to the aws_sns_topic_subscription.civiform_alert_subscription resource
• Removes previously deployed test Lambda resources for auto-confirmation
• Ran terraform plan with auto_confirm_sns_subscription=true to verify it triggers a PendingConfirmation subscription without errors

Checklist

General

• Added the correct label
• Assigned to a specific person or civiform/deployment-system
• Created tests which fail without the change (if possible)
• Performed manual testing (at a minimum run bin/setup without your changes and then bin/deploy with your changes to ensure your changes don't break existing deployments)
• Extended the README / documentation, if necessary

Instructions for manual testing

In your Terraform plan command, pass in:
-var='auto_confirm_sns_subscription=true'
-var='civiform_alarm_email="[email protected]"'

Issue(s) this completes

Fixes #10816