Add support for markdown release notes

[zorgiepoo]

Now that we have a plain text release notes view from #2315 it may make sense to add some subset of markdown support.

Foundation has an API for parsing markdown into an NSAttributedString on macOS 12 or later. It doesn't stylize the text for presentation however, so this would require reading all the presentation intents (NSPresentationIntent) to get things like indentation level, header level, ordinal, and walk through each of the parent intents.. Then creating an attributed string to present this to the text view (maybe using NSParagraphStyle, NSTextTab instances, bullet point characters, etc..). Old systems can fall back to showing plain text.

I don't want to pull in another markdown parser/library dependency so I think utilizing APIs from the OS makes sense.