Add a setting to enable the secondary button style in image-with-text.liquid

[mbarnes-km]

Describe the enhancement you'd like

Each time I update Dawn I need to add the following code to the schema in image-with-text.liquid to enable a secondary color scheme on the buttons.
The CSS for the setting is already there, but the setting cannot be selected from the button-block settings unless I add this code.

Describe alternatives you've considered

I guess the alternative is to manually add this every time, but I don't see a reason this setting shouldn't be available by default.

Additional context/screenshots

In the rich-text section button block this setting is called "Use outline button style" which is a better, more descriptive name than "secondary button style" which I have been using.