[echan & ncai] Compact callout

[eugenechantk]

Checklist

• [N/A] Includes tests
• Update documentation

Changes proposed in this pull request:

• feat(Callout): new compact prop allows using a compact visual appearance

Reviewers should focus on:

Styling of new modifier prop / class

Screenshot

coming soon

[adidahiya]

@eugenechantk I updated this PR:

• pulled in develop
• reverted the H5->H6 change (what was the motivation for this?)
• fixed padding styles in regular & compact mode
• added a "compact" switch to the callout docs example
  • refactored the callout example component to be an FC (ongoing migration as we touch existing code)

[adidahiya]

Note that there is an unrelated bug on develop which has been merged into this PR; I'm working on a fix: #6679

[adidahiya]

Going to merge this for now without the heading size change -- we might consider doing that in a separate PR.