Support end to end reactive workflow

[pellse]

Subqueries (e.g. oneToXXX() functions) are wrapped to be able to participate into a reactive workflow depending on the adapter used (e.g. FluxAdapter, FlowableAdapter, AkkaSourceAdapter), but the subqueries themselves are synchronous by nature (e.g. a database call, a call to a REST service, etc.). It would be nice to support native Publisher e.g. reactive Spring Data Repository (like MongoDB), RSocket, Microprofile Reactive Stream calls, etc.

[pellse]

Fixed in commit 3aa15b0 by adding new modules reactive-assembler-core and reactive-assembler-flux