Add ReactiveSortingRepository support

[ada-waffles]

Currently SimpleR2dbcRepository only implements ReactiveCrudRepository. It does not implement or provide the extra method defined by ReactiveSortingRepository.

Modifying SimpleR2dbcRepository to implement ReactiveSortingRepository would allow consumers to use that interface (and its friends such as CoroutineSortingRepository) when defining their repositories.

I plan to put up a PR for this soon.

This is a follow-up from DATACMNS-1769

Thank you to @mp911de for pointing me in the right direction!