Register R2dbcConverter bean and deprecate ReactiveDataAccessStrategy

[pmaedel]

The docs state that R2dbcConverter is recommended to do most of the work.

R2dbcConverter however must be obtained via ReactiveDataAccessStrategy.
This is fine, but should be documented, as I did expect R2dbcConverter to be readily available as a Bean when being so heavily advertised.

[mp911de]

ReactiveDataAccessStrategy originates from having DatabaseClient using a pluggable data access strategy. Now that DatabaseClient went into Spring Framework and we have a proper R2dbcEntityTemplate, we no longer need ReactiveDataAccessStrategy and can move its parts into R2dbcConverter. A good first step would be exposing getConverter() on R2dbcEntityOperations to align with the other Spring Data modules.

[mp911de]

I repurposed this ticket to align our converter infrastructure with the other Spring Data modules. R2dbcConverter is now registered as bean and ReactiveDataAccessStrategy is deprecated.