[Feature Request] Add italic and small caps options for custom heading styles

[prayidae]

Feature Description
In Style Settings, under Typography -> Headings, add two variables per heading level:

• Font Style (i.e. Italic or Normal; Bold could also be included but is probably redundant with font weight)
• Font variant (small caps or normal)

Miscellaneous Features
N/A

Additional context
These options exist in Minimal and in Baseline. My suggestion for how to structure them is based on Minimal; I am not really attached to the specifics of implementation, I just would like to be able to set headings to be small caps, italic, or both.

The option for small caps exists in Fancy-A-Story but italics does not.

Thank you so much for creating and maintaining this theme which I have found very satisfying to use