Allow evaluation of Rego based policies

[flavio]

Rego policies can be built into WebAssembly modules that can then be evaluated. We have proved this to be possible using this POC

The goal of this issues is to integrate the code of the POC into this crate.

Admission criteria

• Simple OPA policy can be loaded and evaluated by kwctl and policy-server
• Simple Gatekeeper policy can be loaded and evaluated by kwctl and policy-server

Linked cards

• policy-evaluator: evaluate a Rego policy converted to Wasm #15
• Handle Rego policies kwctl#55
• Handle OPA/Gatekeeper policies policy-server#76
• rego support: evaluate most important builtins that have to be implemented host side #16

[flavio]

I think this can be closed right now, at least for Opa policies.

We will create new cards to handle Gatekeeper ones