Add two additional permissions to ProvisionPublishEgressIP policy

[dav3r]

🗣 Description

This PR adds two additional permissions to dns/provisionpublishegressip_policy.tf that are now necessary in order to properly configure the S3 bucket (created in cisagov/publish-egress-ip-terraform) used for publishing egress IPs.

💭 Motivation and context

Without these permissions, we cannot properly configure the egress IP bucket for public read-only access, which is a requirement for cisagov/publish-egress-ip-terraform#6.

🧪 Testing

I applied these changes and verified that I was able to successfully apply the code in cisagov/publish-egress-ip-terraform. All automated tests pass.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All new and existing tests pass.