Provide a way to terminate unfinished requests after graceful shutdown

[ikhoon]

Motivation:

Unfinished requests even after graceful shutdown period are forcivily closed with ClosedSessionException. As ClosedSessionException indicates that the connection was unexpectedly disconnected, ClosedSessionException is not suitable for graceful shutdown.

In this PR, I propose to add ShuttingDownException to terminate unfinished requests when a server stops.

Modifications:

• Introduce GracefulShutdown to customize graceful shutdown behavior.
  • Users can specify a error function to create an exception to unfinished terminate requests.
• Fixed HttpServerHandler to send error responses using the error function of GracefulShutdown
• Fixed Server to send error respones first and then close the connnections.
• Deprecation) ServerConfig.gracefulShutdownQuietPeriod() and ServerConfig.gracefulShutdownTimeout() have been deprecated in favor of ServerConfig.gracefulShutdown().

Result:

You can now use GracefulShutdown to terminate unfinished requests when a server stops.

GracefulShutdown gracefulShutdown =
  GracefulShutdown
    .builder()
    .quietPeriod(Duration.ofSeconds(10))
    .timeout(Duration.ofSeconds(15))
    .shutdownErrorFunction((ctx, req) -> {
        return new ServerStopException();
    })
    .build();

Server
  .builder()
  .gracefulShutdown(gracefulShutdown);

[github-actions]

🔍 Build Scan® (commit: 685f93d)

Job name	Status	Build Scan®
build-ubicloud-standard-8-jdk-8	✅	https://ge.armeria.dev/s/5avgoglum5hfe
build-ubicloud-standard-8-jdk-21-snapshot-blockhound	✅	https://ge.armeria.dev/s/rddielspmilme
build-ubicloud-standard-8-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/om3nvcr76bbv2
build-ubicloud-standard-8-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/646mna2ft3qui
build-ubicloud-standard-8-jdk-17-leak	✅	https://ge.armeria.dev/s/xrfyndh6i3sbw
build-ubicloud-standard-8-jdk-11	✅	https://ge.armeria.dev/s/hefkv7cxtgk2o
build-macos-12-jdk-21	✅	https://ge.armeria.dev/s/rzvbh4stxts6u