[AB2D-6124] Add Opt Out Metrics to Slack Message

[Rwolfe-Nava]

🎫 Ticket

https://jira.cms.gov/browse/AB2D-6124

🛠 Changes

Add more information to the lambda completion slack message with metrics about processed opt out information.

ℹ️ Context for reviewers

I want to make sure my approach here is good. I wanted to avoid going to the database multiple times for performance reasons.

✅ Acceptance Validation

Tested on IMPL environment:

🔒 Security Implications

• This PR adds a new software dependency or dependencies.
• This PR modifies or invalidates one or more of our security controls.
• This PR stores or transmits data that was not stored or transmitted before.
• This PR requires additional review of its security implications for other reasons.

If any security implications apply, add Jason Ashbaugh (GitHub username: StewGoin) as a reviewer and do not merge this PR without his approval.