Venafi + Vault Health Checks

[cdmadrigal]

BUSINESS PROBLEM
As of Vault version 1.13.x, the default pki now supports some health check endpoints. https://developer.hashicorp.com/vault/docs/commands/pki/health-check

This would provide a framework to enhance the backend plugin to support different health checks that may be more relevant to Venafi. i.e: Does the vault pki know if tpp or venafi cloud is available

PROPOSED SOLUTION
Add support for a health check api to allow Vault users or admins to check important information related to the Vault PKI. This may be related to connectivity, health of the service, etc.

CURRENT ALTERNATIVES
N/A