Right/left joins in restriction API

[dstepanov]

It would be nice to have some way to specify (probably a vendor specific) strategy how to access an association.

_Train.manufacturer.navigate(_TrainManufacturer.country).equalTo("Germany")

The manufacturer in this case is an many-to-one association which needs to be joined at some point.
The idea would be to pass the join strategy to the navigate:

_Train.manufacturer.navigate(_TrainManufacturer.country, CustomNavigateStrategies.RIGHT_JOIN).equalTo("Germany")

Right now I have to join it in the Micronaut Data specific way:

    @Find
    @Join("manufacturer")
    List<Train> findTrains(Restriction<Train> restriction);

[otaviojava]

IMHO: it is related to this one here:

#1185

[dstepanov]

This one is more about the restrictions api

[gavinking]

I edited the title for specificity.