What is the problem we are trying to solve here?
The `/` path in our Ember app leads to the `discovery.index` route but
we actually don't render anything on that route leading to a blank page
if the Ember app were to transition to it which is what was happening
when a user adds a custom sidebar section link with the `/` path.
What is the fix there?
Instead of generating a link for the `discovery.index` route when
creating the sidebar section link, we detect if the Ember route is
`discovery.index` and change it to the `discovery.${defaultHomepage()}`
route instead.
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