Update KB ecosystem to use Java fluent api

[sbrossie]

Our code base was started prior Java fluent api, and so we embraced Guava (e.g Iterables.xxx) to perform filtering, sorting, merging operations on data structures - e.g here

We would like to replace all those with new Java syntax and ideally remove guava as a dependency:

object.stream()
                .filter(xxx)
                .***

[sbrossie]

In order to do this, we could work, repo by repo, and then for big repos such as killbill/killbill module by module (and make one PR per module).

[xsalefter]

Additional notes:

• Discussion and resolution about Guava's Event Bus.

• Discussion about Guava's Cache.

• FIXME-1615: DefaultPaginationHelper mean that class if this class refactored, it affect several modules in killbill repository. Thus, fix for this class need to handled by one dedicated PR.

• FIXME-1615 : killbill-client-java : RequestOptions using MultiMap : Exist in killbill-profile-killbill module. This is need work on killbill-client-java.