[CI] Implement "environments" with automatic cleanup

Summary

Let's implement GitLab CI environments so we can ensure that releases are automatically cleaned up upon merge or after a certain amount of time passes (i.e. 4 days).

Example: Charts CI GKE environment

Acceptance criteria

• environment key is added to our jobs that deploy to the clusters
• Environments automatically tear down upon merge or after an agreed-upon amount of time (typically we do 4 days)