Support a handler for checking connection status using Ping frame in HTTP/2

[raccoonback]

Description

In some cases, HTTP/2 connections may remain open even when they are no longer functional. By introducing a periodic Ping frame health check, we can proactively detect and close unhealthy connections.

The Http2ConnectionLivenessHandler schedules and sends Ping frames at a user-defined interval to verify the connection's liveness. If an acknowledgment (ACK) is not received within the specified time, the connection is considered unhealthy and is closed automatically.

However, if other frames are actively being sent or received, the scheduler does not send a Ping frame. This is because the server may delay ACK responses for various reasons. To prevent unnecessary connection termination, Ping frames are only sent when no read or write activity is detected.

Key Changes

1. Added Http2ConnectionLivenessHandler handler to check connection health with Ping frames at a configurable interval.
2. Specify the ping frame ack allowable range through Http2SettingsSpec.

HttpClient.create()
	.protocol(HttpProtocol.H2)
	.secure()            
	.http2Settings(builder -> builder.pingInterval(Duration.ofMillis(100)))

Related Issue

• Fix HTTP/2 PING frame handling #3301