"deep link" headings and icon enhancements

[thescientist13]

Summary

Coming out of #84, one of the enhancements for how deep links were styled were to make the following adjustments

1. Append it to the heading text (so its on the right)
2. Use the plugin configuration to pass the SVG content directly to the plugin

Details

I think we would also want to look into seeing if we could then make better use of the remark-github plugin, which might make sense in release blog posts maybe? Not sure how it really works, tbh.

Otherwise, we can probably get rid of it. 😅

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Unfortunately, this is blocked on until we are able to customize markdown plugins provided to greenwood.config.js