Move Propagator::Options to PropagatorOptions
Propagator::Options does not actually depend on the Propagator type, since the call operator overload is a function template. We can extract it to a separate PropagatorOptions struct.
Closes ACTS-521
Propagator::Options does not actually depend on the Propagator type, since the call operator overload is a function template. We can extract it to a separate PropagatorOptions struct.
Closes ACTS-521