feat: add EKS/RDS Extended Support Eventbridge rules

[georgepstaylor]

This PR adds EventBridge rules and their corresponding targets (SNS) to capture AWS Billing notifications for RDS and EKS Extended Support in the eventbridge.tf file.

EventBridge rules and targets pair:

• Added aws_cloudwatch_event_rule resource for EKS/RDS Extended Support Billing notifications. This rule pattern should capture AWS Billing notifications related to EKS/RDS Extended Support.
• Added aws_cloudwatch_event_target resource links the rule to an SNS topic.

[github-actions]

Pull Request Review Status

• 🖌 Terraform Format and Style: success
• 🔍 Terraform Linting: success
• 👮 Terraform Security Check: success
• 👮 Terraform Security Checkov: success
• 🔘 Terraform Tests: success
• 🔧 Terraform Initialisation: success
• 🤖 Terraform Validation: success
• 🤖 Terraform Example Validation: success
• 📖 Terraform Documentation: success
• 🔖 Commitlint: success

Working Directory: .
Pusher: @georgepstaylor, Action: pull_request
Workflow Run Link: https://github.com/appvia/terraform-aws-alarm-baseline/actions/runs/12889768887

[shanilhirani]

Would we want these to be a conditional resource?

[georgepstaylor]

Would we want these to be a conditional resource?

Good point - have added a boolean flag to disable these in the same way the cloudwatch alarms are.

[shanilhirani]

LGTM