Default theme optional banner(s)

[jasonkuhrt]

Is your feature request related to a problem? Please describe.

I was looking at the default theme extension slots for how to add a banner to the website but didn't find anything ideal. I ended up using nav bar content with some hacky CSS to create a new row, but this doesn't look great yet and it already took me a bit of time so far.

Describe the solution you'd like

I would like there to be a central place to pass some data to a banner content array that when populated will display a strip above the nav bar consisting of a colour and text.

Describe alternatives you've considered

A slot would work too, but lower level. I think banner is common enough to support is as first class data in the theme config?

Additional context

No response

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[brc-dd]

Duplicate of #2071