Add type definition for AthenzX509Config

[hrsakai]

Motivation

Athenz support x.509 certificate and tokenExpirationTime param has been removed at https://github.com/apache/pulsar-client-cpp/pull/274 .

Modifications

• Add type definition for athen x.509 certificate

• Mark tokenExpirationTime as deprecated

Verifying this change

• [x] Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Documentation

• [x] doc-required (Your PR needs to update docs and you will update later)

• [ ] doc-not-needed (Please explain why)

• [ ] doc (Your PR contains doc changes)

• [ ] doc-complete (Docs have been already added)

[massakam]

I think the following page needs to be updated, so I'll label it as doc-required. https://pulsar.apache.org/docs/next/security-athenz/

[massakam]

The document has been updated by https://github.com/apache/pulsar-site/pull/747.