AppDynamics Plugin

### Where is the problem?

Source: https://docs.konghq.com/hub/kong-inc/app-dynamics/

SSL can be configured using KONG_APPD_CONTROLLER_USE_SSL environment variable. However, there is no way to set the SSL directory and filename thus we assume it will take the default certificate of the OS "/etc/pki/tls/certs/ca-bundle.crt". However upon onboarding the plugins using the environment below, we encounter an SSL handshake error.

export LD_LIBRARY_PATH=${LIBRARY_PATH}
export KONG_APPD_CONTROLLER_HOST = ${APPD_HOST}
export KONG_APPD_CONTROLLER_PORT = 443
export KONG_APPD_CONTROLLER_ACCOUNT = ${APPD_ACCOUNT}
export KONG_APPD_CONTROLLER_ACCESS_KEY = ${APPD_ACCESSKEY}
export KONG_APPD_APP_NAME = ${APPNAME}
export KONG_APPD_TIER_NAME = ${TIERNAME}
export KONG_APPD_NODE_NAME = ${NODENAME}
export KONG_APPD_LOGGING_LEVEL = 0
export KONG_APPD_LOGGING_LOG_DIR = ${LOG_PATH}

### What is your suggestion?

I suggest to include the option for certificate particularly for on-premise environment that requires certs to post metrics in AppDynamics controller.

### Code of Conduct and Community Expectations

- [X] I agree to follow this project's Code of Conduct
- [X] I agree to abide by the Community Expectations

Start with the AppDynamics plugin documentation at docs.konghq.com/hub/kong-inc/app-dynamics/ and review how KONG_APPD_CONTROLLER_USE_SSL is documented. Confirm where certificate directory and filename settings are defined and how on-premise SSL failures should be handled; done means the supported certificate option and its usage are documented or implemented for the plugin.

Written by the indexing model from the issue text.