Right/left joins in restriction API

Nobody has claimed this yet.

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 findTrains(Restriction restriction);
```

Start by reviewing the restriction API's navigate association shown in the issue and compare it with the Micronaut Data @Join example. Determine how a caller would specify right or left join strategies and which API and provider behavior must support them. Done means the strategy can be expressed through navigate and its expected join behavior is covered.

Written by the indexing model from the issue text.