Implement Policy Enforcer Plugin

- Added a new Policy Enforcer plugin to evaluate incoming messages against OPA policies.
- Configurable via YAML with options for policy sources, actions, and query.
- Integrated into existing configuration files for BAP and BPP.
- Updated related tests and documentation for the new functionality.
- Enhanced plugin manager to support Policy Enforcer instantiation.

install/build-plugins.sh

@@ -23,6 +23,7 @@ plugins=(
     "schemav2validator"
     "signer"
     "signvalidator"
+    "policyenforcer"
 )
 
 for plugin in "${plugins[@]}"; do