Right now, we're working on making REST modules as a separate clean list that users can pick from, for ease of use and context separation. At the moment, the default view in all instances is the MediaWiki Rest API (routes not in modules) view, which displays the default routes in mediawiki core.

However, as we add modules into the system, it would be helpful to be able to specify a specific module for the default view. This would enable us to show different starting state for the Sandbox in different instances; for example, Wikifunctions can display its own REST module by default in its wiki, wikidata its module in its wiki, while other wikis in productions show the default core routes.

Deliverable: Allow specifying (or overriding) the default module that is loaded per instance for Special:RestSandbox.