Issue-1074: Add Support for an Aside Component (release/v2.5.0)

[mogmarsh]

Description

It's a common pattern for publishers to include a sidebar or aside element to appear alongside their content, which doesn't translate well (if at all) into Apple News format. Since this is custom functionality, we will need a way to map custom sidebars or aside elements to this new component:

1. Create a new Aside component
2. Add a configuration option to let publishers enter a CSS class that denotes content that should be incorporated into the new Aside component
3. If a container is encountered that has the specified class, it should be incorporated into the new Aside component rather than whatever it would have been otherwise
4. Add new theme settings to determine what the appearance of the Aside component should be, with sensible defaults for the default theme and the sample themes that ship with the plugin; the component should be visually distinguishable since on mobile it will appear between paragraphs; also allow alignment to be set (left/right)
5. Configure display for the component so that text wraps around it on larger viewports but it appears between paragraphs on small viewports

Use Case

When a publisher uses an aside or sidebar component in their article body, it should be properly reflected in Apple News.

Issue Link

Add Support for an Aside Component

[kevinfodness]

Needs a test, but can follow up with a separate PR for that. 🍣