integration test cleanup function

[jchrostek-dd]

Overview

• Personal stacks used for integ testing don't always get cleaned up. We had a lot of LMI stacks that was causing us to hit our Capacity Provider limit and not deploy new integ stacks for testing.
• This PR creates a lambda function that runs daily and deletes integration stacks that haven't been updated in 7 days.

Testing

• Deployed function and invoked it. Confirmed that it deleted old stacks.

[duncanista]

Feels like an unnecessary project when we could just have a lambda that cleans all resources in our account which might not be needed – or projects which failed to delete

[jchrostek-dd]

Feels like an unnecessary project when we could just have a lambda that cleans all resources in our account which might not be needed – or projects which failed to delete

I'm a bit concerned that if we do this across all of stacks in the entire account, we could accidentally delete stacks we meant to keep. I'm fine if we want to revisit this in the future, but I don't think it hurts to add a integration-test specific stack cleanup for now since we are seeing flaky integ tests as a result.