Support highlighting callout quote markers

[MeanderingProgrammer]

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Follow up to: https://github.com/MeanderingProgrammer/markdown.nvim/commit/43bbefd410333a04baf62ddfa8bb2a2d30a1bbc1

While we are able to add the text overlay on callouts the quote marker itself always uses the same highlight group rather than matching the highlight of the callout.