EuiModal Improve design of scrolled content

[ryankeairns]

While we aim to keep the content of modal relatively short and focused, it can become scrollable.
Currently, it is not obvious when content scrolls behind the footer as there is do distinct, visual cue to separate the footer.

See this thread for additional context.

Possible solution
When content becomes scrollable, apply a pattern like the one used in the flyout footer - either a shaded fill and/or slight gradient along the top edge. (Update: there is a gradient along the edge but its barely noticeable... see above)