http2: add ping event

Add a `Http2Session` event whenever a non-ack `PING` is received.

Fixes: https://github.com/nodejs/node/issues/18514

PR-URL: https://github.com/nodejs/node/pull/23009


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>