Preferred block size for bind joins per fed.member

For every federation member with an interface that supports some form of bind join, it should be possible to set/observe (live!) and get the preferred block size for the bind join requests. Notice that this number may even be different for different types of bind join requests (e.g., using VALUES versus FILTER etc). Additionally, the way this would be implemented should not affect other types of join operators (e.g., index nested loops joins).

Start by tracing the fed.member interfaces and the bind-join implementation, then compare how VALUES and FILTER requests are handled with index nested loops joins. Done means each supported federation member can expose and update the preferred block size live, with separate values where request types require it, without changing other join operators.

Written by the indexing model from the issue text.