Sidebar - panel/content should support padding

[mcoker]

trafficstars

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. Seems like the sidebar should support padding/insets with body elements like similar components or maybe we can officially extend page sections to work in other components like this. We likely want to support all of the things page sections allow - insets, background colors, grow/fill, etc.

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