Sidebar - panel/content should support padding

[mcoker]

From https://github.com/patternfly/patternfly/pull/5088/files, we're adding page sections in the sidebar to create padding - while that works, we should probably rethink that.

The sidebar should support padding/insets with body elements like similar components (Drawer)

Seems like having a vertical divider between sections is also going to be a common enough use case that the component should likely support that as well.