Rego extension function to return public keys for a given namespace

Create Rego extension function (or modify the existing one) that retrieves public keys from the Signer service by sending a specific key namespace and optionally a specific key name. If the specific keyname is skipped, all keys from the given namespace should be returned.

Example usage:

keys := keys.get(namespace, keyname)

Acceptance Criteria

• Implementation
• Unit tests