clarify usage of prerender option in relation to Renderer plugins

[thescientist13]

Summary

Coming out of discussions / feedback related two ProjectEvergreen/greenwood#1343, it was the takeaway that it probably doesn't make much sense to have to settings for the same thing. If the user wants to enable prerendering, the single configuration option in greenwood.config.js should be sufficient. Since the plugin has access to the compilation and all its options, it can derive its behavior / support based on that and / or in its documentation.

Details

So the goal here should be to just align with the new convention we're setting going forward and update the Renderer Plugin API docs accordingly - https://greenwoodjs.dev/docs/reference/plugins-api/#renderer