Create 6845-add-a-parameter-for-scroll-speed.md

[AndriyFedorovich]

This MR is a proposition to implement a parameter for scroll speed animation in methods like scrollTo

[AndriyFedorovich]

Press ❤️ if you support

[okwasniewski]

I think on iOS this can be achieved pretty easily using animateWithDuration.

I've modified the code of RCTScrollView with this snippet and it works. I think providing a native way of handling this will be really nice addition to the Framework:

[UIView animateWithDuration:10.0f delay:0 options:UIViewAnimationOptionCurveLinear animations:^{
      self->_scrollView.contentOffset = offset;
    } completion:NULL];