Add more information about http2 connection

[polRk]

Is your feature request related to a problem? Please describe.

CONTEXT

Within the YDB SDK, client-side load balancing is used. We send a single request to any database node, and it returns an array of available endpoints. Our task is to maintain connections to these endpoints as needed: close connections that we no longer need to use, create new connections to those that are missing, balance requests across these connections, and have the ability to send a request to a specific connection.

PROBLEM

Currently, it's not very clear how to properly close a connection (graceful shutdown), how to obtain the status of a connection, and how to receive notifications when a connection has been closed.

ONLY FOR HTTP2

Describe the solution you'd like

Extends Transport with EventEmitter, emit information about transport status changes, add current status of connection.

Additional context https://ydb.tech/docs/en/recipes/ydb-sdk/balancing https://blog.ydb.tech/client-side-balancing-in-ydb-89677b34fd5b