Add repo security scanner to CI

[menge101]

https://github.com/UKHomeOffice/repo-security-scanner

Checks for credentials, secrets, etc checked into repo, should be an easy add to CI

[menge101]

Evaluate that one versus these:

https://github.com/awslabs/git-secrets
https://github.com/zricethezav/gitleaks

[osterman]

This is a great suggestion. We'll work towards implementing it, but may take a while. We'll start by adding a couple of the utilities to our cloudposse/packages distribution and then integrate it into our cloudposse/build-harness.