DDLS-408 add dynamodb kms key part 1 of 2

[jamesrwarren]

Purpose

Adding CMKs to dynamodb tables

Fixes DDLS-408

Approach

Part 1 of 2. Create the CMK and we can already add it to cleanup job dynamo table as ci already has ability to decrypt it.

However we can't add to the other one till we give the lambda permission which will be in part 2.

I've also added description to SG rules. This does recreate them but they're very quick to recreate.

Learning

NA

Checklist

• I have performed a self-review of my own code
• I have updated documentation (Confluence/ADR/tech debt doc) where relevant
• I have added tests to prove my work
• The product team have approved these changes
• I have checked my work for potential security issues and refered to the OWASP top 10

Frontend

• I have run an in-browser accessibility test (e.g. WAVE, Lighthouse)
• There are no deprecated CSS classes noted in the profiler
• Translations are used and the profiler doesn't identify any missing
• Any links or buttons added are screen reader friendly and contextually complete
• If adding GA events, I have updated or checked the existing category or label values