Add JGroups integration for Spring Cloud Bus - #3299

Overview

This PR adds JGroups support to Spring Cloud Bus, allowing applications to use JGroups as a transport for propagating RemoteApplicationEvents between cluster members.

Changes

• Add a new spring-cloud-starter-bus-jgroups module.
• Add JGroups dependency management with JGroups 5.5.7.Final.
• Implement JGroupsBusBridge for sending and receiving Bus events over JGroups.
• Add configurable JGroups cluster name through spring.cloud.bus.jgroups.cluster-name.
• Add JGroups auto-configuration with appropriate Bus and classpath conditions.
• Back off when another BusBridge is already configured.
• Register the JGroups auto-configuration through AutoConfiguration.imports.
• Add tests covering:
  • JGroups Bus bridge creation.
  • BusBridge back-off behavior.
  • Event serialization and transmission.
  • Event deserialization and delegation.
  • Configured cluster name.
  • Channel lifecycle/close behavior.

Configuration

The default cluster name is:

spring:
  cloud:
    bus:
      jgroups:
        cluster-name: spring-cloud-bus