Support the runner-requested-split path for SDF

[pabloem]

This does not include adding dynamic splitting of work - instead, this only means setting up the data/request path with a pre-provided split manager like in FnApiRunnerTest.

[pabloem]

I'll take on this issue as well.

[valiantljk]

@pabloem you can assign to me

[pabloem]

@valiantljk I will get some pointers to look at this : )