Kong Identity: Implement JWT client authentication

## Jobs to be done (optional)
Benefits
Enhanced Security: Using a private key for signing eliminates the need to transmit a client_secret over the network, reducing the risk of credential leakage.
Non-repudiation: The client cannot deny having made the request because it was signed with their unique private key.
Stateless Validation: Resource servers can validate the access token locally using the issuer's public key without needing to constantly check a central database, which improves performance and scalability in microservice architectures.

This mechanism is widely used in ecosystems like Open banking.

## Definition of done
- Convert draft from eng to how to or reference guide

## Information
DRP: Andrew J.
Aha: https://konghq.aha.io/features/KID-12

## Due date (optional)

## Size