Add Custom elements to Experimental Sidebar

[mcdanlj (Michael K Johnson)]

@mcwumbly

We’re planning to add a single “custom section” feature in the not-too-distant future, which would allow you to add arbitrary named links to things within your own site.

I like this idea.

My largest site uses custom header links that would likely make as much or more sense in a sidebar custom section in the long run. Of our three links there, one is to a sibling site (mastodon node) and two are internal to the discourse site itself. Not needing custom header links for that would I think be visually cleaner, keeping related information together.