♻️ Standardise mandatory AWS resource tagging across deployments

[jasonBirchall]

👀 Purpose

• Implement the GDS mandatory AWS resource tagging strategy across all Terraform deployments
• Ensure consistent cost allocation and resource management through standardised tags
• Align documentation with actual implementation and provide a template for future deployments.

♻️ What's changed

• Added complete AWS provider default_tags to opensearch and chat deployments (previously had no tagging).
• Added missing mandatory System tag to govuk-publishing-infrastructure deployment
• Added missing Environment tag to GitHub deployment
• Standardised cluster-infrastructure and cluster-services to use local pattern for cleaner tag management
• Updated terraform/docs/tagging-guide.md to reflect mandatory tags (Product, System, Environment, Owner)
• Created terraform/docs/tagging-template.md with standardised tagging patterns for future deployments

📝 Notes

• All 19 AWS deployments now have the 4 mandatory tags: Product, System, Environment, Owner
• 3 deployments still need minor fixes: search-api-v2 (missing all tags), vpc (regional providers), cloudfront (global provider)
• Template follows AWS provider default_tags best practice for automatic tag inheritance
• No breaking changes - all new tags are additive and applied at the provider level

[AgaDufrat]

@jasonBirchall are you still working on this? Shall we convert it to Draft until you have time, so it doesn't pop up in our Seal notifications?

[jasonBirchall]

Hey, Aga. I’m still working on the final PRs to get this change in. I'm at the point where the TF plans look a little hairy now, so wish me luck. 😝