feat(cloud-formation): Preserve existing tags

[akash1810]

What does this change?

Update the cloud-formation deployment type to preserve any existing tags on the CloudFormation stack.

How to test

1. Deploy main to RIff-Raff CODE
2. Add a random tag ¹ to the stack playground-PROD-cdk-playground in the Developer Playground account (from https://github.com/guardian/cdk-playground)
3. Using Riff-Raff CODE, deploy the project devx::cdk-playground
4. Observe the tag added in step 2 being removed
5. Deploy this branch to Riff-Raff CODE
6. Repeat step 2
7. Repeat step 3
8. Observe the tag added in step 6 remaining, and the deployment log stating as such

Screenshot

Footnotes

1. I added the tag Month -> September ↩

[github-actions]

Deploy build 3465 of tools::riffraff to CODE

All deployment options

• Deploy build 3465 of tools::riffraff to CODE
• Deploy parts of build 3465 to CODE by previewing it first
• What's on CODE right now?

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From guardian/actions-riff-raff.