Enable Pulsar authentication for Client authentication using private_key_jwt method

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Motivation

The motivation for this enhancement stems from the need to bolster security and efficiency in Pulsar’s client authentication. The private_key_jwt method offers a secure means for client authentication, utilizing a private key and JSON Web Token (JWT). By implementing this method, Pulsar can enhance its security framework.

### Solution

The proposed solution involves enabling Pulsar authentication for Client authentication using the private_key_jwt method.

Related materials:

For further details on the private_key_jwt method, refer to the specification outlined in https://kb.authlete.com/en/s/oauth-and-openid-connect/a/client-auth-private-key-jwt

### Alternatives

While evaluating alternatives, the current OAuth2 flow with client credentials (client_id and client_secret) was noted. This in our case is not an option, since we use the flow with client_assertion_type and client_assertion.

Implementing the private_key_jwt method offers a more secure and efficient alternative, reducing dependency on client_secret and providing enhanced security through private key and JWT-based authentication.

### Anything else?

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start by reviewing Pulsar’s existing OAuth2 client-credentials authentication flow and the private_key_jwt specification linked in the issue. Determine the client authentication entry points affected and define done as supporting client_assertion_type and client_assertion without relying on client_secret.

Written by the indexing model from the issue text.