Reactive support

[jordanst3wart]

Feature request, porting it initially from here: derjust#138

It would be great having support for the reactive spring boot stack.

Currently, i'm getting:

org.springframework.dao.InvalidDataAccessApiUsageException: Reactive Repositories are not supported by DynamoDB. Offending repository is com.example.app.repository.ItemRepository!

The repository looks like:

package com.example.app.repository;

import com.example.app.model.Item;
import org.springframework.data.repository.reactive.ReactiveCrudRepository;
import reactor.core.publisher.Mono;

// ReactiveSortingRepository maybe and pageable
public interface ItemRepository extends ReactiveCrudRepository<Item, Integer> {
  Mono<RawItem> findRawItemById(Integer id);
}

[jordanst3wart]

I thought this would be easy, but it locally looks like a lot of work. Here is the repo for h2: https://github.com/r2dbc/r2dbc-h2