Allow to set different button styles for "call to action" button in header overlay

[Andre601]

Right now does the header.actions list only allow/accept these options:

• label for the text to display
• url for setting the target URL

This is extremely limiting when it comes to designing since you only have a single button style that may not even look that good depending on images or bg colours used.
I would love if the section could receive a btn_class option similar to a feature_row or perhaps other ways to add classes for the styling/behaviour.

If this is already a thing should the docs be updated, as they only mention those two features... if at all (The docs are honestly quite vague about available options and not really informative regarding the splash-style page options)