Add potential for subheaders and extra body content to Sources card

[rebeccaalpert]

IFD is looking to add additional content types to Sources card

We should allow these other fields in the card for custom content injection, and add tests.

We should create some demos on how this could be accomplished as well.

A11y notes:

• For the label/badges that denote “confidence levels,” just ensuring that the context of what the percentage means isn’t lost is important, whether that’s having the word “confidence” or similar visually rendered, or putting it inside SR text for AT

Design kit issue: patternfly/patternfly-design-kit#890