Feature/eja eli 343 adding deletion protection and ig public access block

[eddalmond1]

Description

Adding Terraform changes to address two of the issues highlighted in AWS SecurityHub - see https://nhsd-confluence.digital.nhs.uk/spaces/Vacc/pages/1132925310/Security+Audit+-+Preprod+-+Preparation+for+Pen+Test for all issues highlighted.

Specifically, this PR:

1. Restricts VPCs from using Internet Gateways to access the public internet. There is a risk that this might 'break' our API Gateway - I've found conflicting advice in the AWS documentation, so the only way to know for sure is to deploy this change and check everything works as intended.
2. Adds deletion protection, in Production only, to the dynamoDB table we create.

Context

It addresses two Medium severity security issues.

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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