Leverage (Reactive)SessionRepositoryCustomizer for SessionRepository customization

[vpavic]

Spring Session core recently introduced strategies for customizing SessionRepository and ReactiveSessionRepository without having to manually define those beans and therefore lose all the capabilities that configuration infrastructure supports.

See spring-projects/spring-session#1499 and spring-projects/spring-session@df3e4c5b.

[jxblum]

This already somewhat exists since SSDG already included a SpringSessionGemFireConfigurer interface for such concerns.

However, I do see that the o.s.s.config.SessionRepositoryCustomizer is slightly different by design too.

Will add GemFire/Geode-specific SessionRepositoryCustomizer as another option.