Add OPA Scan

The DevOps Quickstart tool uses Open Policy Agent (https://www.openpolicyagent.org/) to "define and enforce policies on infrastructure resources at development time."

We should look at adding this tool to the Golden Pipeline.

https://github.com/aws-samples/devsecops-quickstart/blob/main/devsecops_quickstart/opa_scan/opascan.py

Start by reading the linked devsecops-quickstart/devsecops_quickstart/opa_scan/opascan.py implementation and then inspect this repository's Golden Pipeline entry points. Identify how a new scan is integrated and what existing pipeline tests cover. Done means OPA scanning is integrated into the Golden Pipeline with appropriate coverage and documented behavior.

Written by the indexing model from the issue text.