[TTAHUB-2749] Add github-slack workflow for production PR notifications

[kryswisnaskas]

Description of change

Added a GitHub action that will send notifications to the github integration test channel when the production PR is ready for a review.
Added a notification in the CI/CD pipeline to send a slack notification on successful deployment.

How to test

This will need to be merged, and a PR for production will need to be ready for review for the workflow to be triggered.

Issue(s)

• https://jira.acf.gov/browse/TTAHUB-2749

Checklists

Every PR

• Meets issue criteria
• JIRA ticket status updated
• Code is meaningfully tested
• [n/a] Meets accessibility standards (WCAG 2.1 Levels A, AA)
• [n/a] API Documentation updated
• [n/a] Boundary diagram updated
• [n/a] Logical Data Model updated
• [n/a] Architectural Decision Records written for major infrastructure decisions
• [n/a] UI review complete

Before merge to main

• OHS demo complete
• Ready to create production PR

Production Deploy

• Staging smoke test completed

After merge/deploy

• Update JIRA ticket status

[AdamAdHocTeam]

Not sure how to test but looks good.