Plugins: custom category renderers

[connorjclark]

Just like we have customer renderers for perf and pwa, so should plugins.

See #9051 (comment)

[brendankenny]

I'll warn up front that because of the way we support sharing and rendering lighthouse results, this is either difficult to pull off or an XSS waiting to happen, so I think this is unlikely to work out, at least at the level of flexibility you might be imagining.

Expanding the core category/details renderers to be able to display what you'd like to put in a report is likely to be a lot more fruitful.

[brendankenny]

Not feasible today, but we can explore at some point in the future. For now, let's focus on improving the primitives available in categoryRenderer and detailsRenderer.